Transcript Science Solid Tumors webinar on 11 June 2014 Solid... · 3 I'll start by formulating the...
Transcript of Transcript Science Solid Tumors webinar on 11 June 2014 Solid... · 3 I'll start by formulating the...
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Solid Tumors Reveal Their Secrets: Predictive and Prognostic Evidence
from Copy Number Analysis Webinar
11 June 2014 [0:00:00] Slide 1 Sean Sanders: Hello and a very warm welcome to this Science/AAAS audio webinar. Slide 2 My name is Sean Sanders and I'm the editor for Custom Publishing at Science. In today's webinar, we'll be discussing the importance of copy number
variation analysis in cancer, particularly in solid tumors. Detection of copy number aberrations is becoming increasingly important for tumor profiling in order to not miss genetic changes potentially not detected by other means including next generation sequencing.
Moreover, whole‐genome copy number analysis can play a critical role in
identifying clinically‐relevant, prognostic, and predictive biomarkers. Biomarker identification and validation is technically challenging especially when using formalin‐fixed, paraffin‐embedded tissue or heterogeneous samples where only a small fraction of the cells may be aberrant.
This webinar will explore the importance of copy number analysis and
highlight new technologies that are making this process more accessible especially in solid tumor samples. It is my great pleasure to introduce to you our guests for today's webinar. They are Dr. Paul Boutros from the Ontario Institute for Cancer Research in Toronto, Canada and Dr. Ajay Pandita from Core Diagnostics in Palo Alto, California, a warm welcome to you both and thank you both for being on the line with us today.
Before we get started for today's webinar, as always, we have some
information that our audience might find helpful. Slide 1
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You can change the size or hide any of the windows in your viewing console.
The widgets at the bottom of the console control what you see. Click on these to see the speaker bios or additional information about technology related to today's discussion, or to download a PDF of the slides.
Each of our speakers will give their presentations after which we will have a
Q&A session, during which we will address some of the questions submitted by our live online viewers, so if you're joining us live, start thinking about some questions now and submit them at any time by typing them into the box on the bottom left of your viewing console and clicking the "submit" button. If you can't see this box, click the red Q&A widget at the bottom of the screen.
Please do remember to keep your questions as short and clear as possible as
that will give them the best chance of being put to our panel. You can also log in to your Facebook, Twitter, or LinkedIn accounts during the webinar to post updates or send tweets about the event. Just click the widgets on the bottom of the screen. For tweets, you can add the hashtag #ScienceWebinar. Finally, thank you to Affymetrix for their sponsoring of today's webinar. Now, I'd like to introduce our first speaker for today, Dr. Paul Boutros.
Slide 3 Dr. Boutros is a principal investigator in informatics and biocomputing at
OICR, and an assistant professor in the Departments of Pharmacology & Toxicology and Medical Biophysics at the University of Toronto. His research focuses on personalizing therapy for prostate cancer by developing novel statistical methodologies.
He is leading the bioinformatics analysis of 500 prostate cancers as part of
the Canadian Prostate Cancer Genome Network and is using these data to develop biomarkers for intermediate risk prostate cancer.
A very warm welcome to you, Dr. Boutros. Dr. Paul Boutros: Thank you, Sean, and thank you for the organizers for inviting me to talk to
you today. I'm going to speak to you about intermediate risk prostate cancer and how we can use copy number aberrations to understand it better.
Slide 4
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I'll start by formulating the general problem that we face in personalized medicine studies and then move to a couple of vignettes about intermediate risk prostate cancer.
Slide 5 The core problem that we face in almost any cancer personalization studies is
that patient outcome is highly variable and you see that here in this plot of survival outcome for early stage lung cancer, and this is true for pretty much any tumor type. We have a number of patients who will suffer an event early in their progression into the disease and other patients who will live for many years after treatment.
Slide 6 What we would really like to do is to be able to identify those groups a priori
so that we could offer personalized treatment to them, giving more treatment to the groups that will have an early event and less treatment to those that will have later events. In particular, I've exposed this as if it's a two‐group problem. It's really a continuous one and we're focusing on this easier dichotomization now, but eventually we'd hope to give each patient the therapy that's most appropriate to them.
Slide 7 Now, this is not a new idea by any means. It's one that's been longstanding in
the field and the older hypothesis has been that there are a distinct number of tumor subtypes which have very distinctive molecular profile. Those distinctive molecular profiles lead to distinct prognoses or clinical outcomes. And from a computational biology perspective, this screams a class of techniques called pattern discovery.
Slide 8 The first application of pattern discovery was into solid tumors within breast
cancer where there was some classic work that identified five distinct subtypes, the subtypes that we still know and use today.
Slide 9 And very importantly, those subtypes are associated with different types of
outcome. [0:04:57]
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For example, if we focus on the panel on the left, the top blue curve with
about 90% eight‐year survival is the Luminal A subtype of breast cancer. The red curve where all patients have passed on after just four years is the basal subtype. And so, we see that there are clear, distinct molecular subtypes with clinical differences. This is importantly reproducible.
Slide 10 For example, I'm showing you a 600‐patient validation study by Rob
Tibshirani's group and there've been many other such validation studies showing that these are identifiable in labs around the world. Unfortunately, this doesn't turn out to be true for most other tumor types.
Slide 11 At almost the exact same time, David Beer's group in Michigan was
identifying clusters that are associated with lung cancer and that defined different subtypes of lung cancer, which had very distinctive outcome. Unfortunately, they could not reproduce another data set largely due to technical reasons.
Slide 12 Similarly, a group from Duke showed some truly remarkable differences in
outcome associated with some Bayesian modeling technique. Unfortunately, that study turned out to be fraudulent and it was retracted. I guess what we really found is that the fundamental problem we have in most tumor types is that there are too many subtypes.
Slide 13 This is well exemplified in lung cancer whereas this heat map shows, you can
see dozens or hundreds of different tumor subtypes that are present even just defined by a small set of fixed genes.
Slide 14 This explains something that our statistical colleagues have been telling us
for years, which was that the patient cohort sizes that we were using weren't sufficient for robust biomarkers, that in reality, we should have needed thousands of patients to identify these good genomic biomarkers.
Slide 15
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And so, in a way, the field pivoted and in the mid‐2000s, people started
redefining the problem saying that there's a large number of tumor subtypes and their molecular profiles were overlapping instead of distinctive, but these still lead to distinct clinical outcomes. This, of course, indicates machine learning techniques would be appropriate and there's been a large series of work to optimize the use of machine learning techniques.
Slide 16 I'll kind of summarize the field by saying that we can essentially take any
single type of data and maximize our information retrieval from it, so modern mRNA based markers are able to use 99.9% of the information available, but it still doesn't achieve what you might consider clinically useful results.
Slide 17 This is what was up until a couple of years ago, the state‐of‐the‐art for lung
cancer biomarkers, and you can see it does a reasonable job. There are differences between a survival curve, but unfortunately, this corresponds to about a 66% accuracy of predicting good versus poor outcome. The patient isn't going to accept being told, "Oh, maybe I don't need chemotherapy because you're two‐thirds confident in your prediction." Rather, we need to be able to make robust predictions.
Slide 18 And in some sense, this is the origin of a lot of large multimodal studies. The
idea was that we would want to move beyond just using a single data type at a time. We'd want to create accurate algorithms that can work robustly, that could handle diverse types of data in an intricate way that would handle diverse problems and that would incorporate what we know about clinical features directly into the modeling.
In fact, in a lot of healthcare systems, you'd want these models to actually
incorporate treatment options and even payment options, cost considerations. And of course, it has to be fast. It should be able to run in a day from standard biopsy‐type samples. So in some sense, this is the origin of large multimodal projects like the ICGC or the TCGA.
Slide 19 What I'll talk to you also is within the framework of one of the ICGC projects
called the Canadian Prostate Cancer Genome Network.
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Slide 20 This is a project that's co‐led by four people ‐‐ Rob Bristow, a radiation
oncologist; John McPherson, a genomicist; Theo van der Kwast, a pathologist; and myself, a computational biologist, and we're tackling prostate cancer.
Slide 21 In Canada, that affects 25,000 people a year, about 250,000 in the US.
Unfortunately, only about one in six or one in seven of those will succumb to their disease.
In fact, we often suffer from an overdiagnosis of prostate cancer, and that's
really clear in this incidence graph where you can see a sharp peak in the early 1990s corresponding to the introduction of PSA screening. By contrast, there's only a slight decline in mortality and this is something that's very important to address.
Slide 22 In general, prostate cancer is considered or diagnosed and prognosed
through a series of quite simple tests. There's a digital rectal exam, which is used to initially detect a large majority of tumors supplemented by imaging, biopsies to confirm the presence of tumor and grade it, and PSA testing both for screening and to allow us to identify patient prognosis.
Based on those criteria, we classify patients into low, intermediate, or high
risk groups if they have localized disease, and we selected to focus on the intermediate risk group.
Slide 23 The intermediate risk group is defined by Gleason 7 scores. [0:10:02] These are measure of how differentiated the cells are, how they look under a
microscope, and it's really taking a look at the two largest areas of the tumor and asking what are the Gleason scores of those two regions.
Slide 24
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When you do so, you can divide patients into these low, intermediate, and the high risk groups and you can see that they're treated with different modalities. Low‐risk patients are generally just surveilled to see if their disease will progress. High‐risk patients receive treatment plus additional therapy.
At the intermediate risk group, our goal is to move a large fraction of these
patients into high risk saying about one‐third of them are actually going to succumb to their disease and have a recurrence. Can we figure out who those are in advance and give them additional treatment, and can we identify those patients who are actually low‐risk and their disease doesn't even need any treatment at all? Therefore, we want to substage or substratify the intermediate risk group for prostate cancer patients.
Slide 25 And so, what have we been doing to try to address those questions? Well,
the first thing that we explored was the internal heterogeneity of Gleason 7 prostate cancer.
Slide 26 What you're seeing here are copy number profiles of the entire genome
going from Chromosome 1 at the left to the Y chromosome on the right for Gleason 7 prostate cancer, and there are two groups. The top in dark orange is Gleason 4+3 and the bottom is Gleason 3+4, and you can immediately see a series of recurrent abnormalities and well‐known genes like NKX3‐1 and MYC, and we wanted to investigate these in a bit more detail.
As soon as we started looking at these array‐based copy number profiles
derived from biopsy specimens, we immediately noticed some things we didn't expect. So we started focusing on the subset of samples ‐‐ and I'll talk about some genome sequencing results from those in a moment ‐‐ but one of the most interesting things that we saw was a very unexpected finding in the amplification of a gene called MYCL or LMYC.
Slide 27 The MYC family of oncogenes is well‐known to be associated with a large
number of tumor types and it's recurrently amplified in prostate cancer. Previously though, small focal amplifications in LMYC had not been reported. We identified these in almost a quarter of our patients and very intriguingly they're exclusive with amplifications in CMYC or to a lesser extent, NMYC.
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That's very interesting because the MYCs are known to have an autoregulatory function, which prevents multiple MYC genes from being highly expressed in a single cell. Additionally, you can see here that MYCL amplification is strongly associated with p53 deletion.
Slide 28 We went to explore this in a bit more detail and that first we actually didn't
believe the array analysis because it was so sensitive, and we went ahead and did real‐time PCR and subsequently FISH, and we were able to confirm that the arrays were picking up focal amplifications to three, four, or five copies in this single gene with a very small, minimally amplified region.
Slide 29 We found that this is associated with genomic instability that LMYC‐amplified
tumors have a significantly larger fraction of the genome that's altered by copy number aberrations.
Slide 30 And in a very unusual way where rather than having a few large
amplifications, they have a large number of small deletions and amplifications.
Slide 31 The gene itself is weekly prognostic. It predicts patient survival to a modest
extent. Slide 32 And maybe most interestingly, it's associated with a very unique mRNA
profile. So from this copy number array analysis, we're immediately able to identify a single gene that defines a subtype of prostate cancer that was previously unrecognized.
Slide 33 Now, we went ahead to say next we want to take a look at the internal
heterogeneity and here we linked copy number aberration assessments using arrays to SNV and rearrangement assessment using sequencing analysis, and what we did is we focused on a small number of tumors and we looked internally at their heterogeneity.
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Slide 34 So what we really did is we sliced through the prostate at many different
layers and at each layer, we would take a look in detail or a pathologist would take a look in detail at all of the different regions of tumor.
Slide 35 You'd see in this type of plot that there is a subset of the tumor in the
bottom left that's purple. It's mixed Gleason pattern 3 and 4, and we micro‐dissect out that spot and we'd give array and sequencing analysis on it. Similarly, the little blue spot above it that's about 5% Gleason 4 would be dissected and separately sequenced and analyzed.
Slide 36 The net effect of this is it allows us to assess the internal heterogeneity in
prostate cancer. Now, what you're seeing here is a fairly complex slide. Let's just focus initially on the box itself. This box defines nine regions taken from a single man's tumor and you can immediately see striking variability in the number of point mutations. One region of the tumor has about 150. Another region has only about 15, so in order of magnitude.
[0:15:01] Similarly, this other box describes another set of five regions from a single
man's prostate and again, you see an order of magnitude difference in the number of point mutations, protein coding point mutations seen from region to region.
Slide 37 That's not just true at the level of point mutations. You can see in the top
panel here the number of copy number aberrations. And in the last group of five, you can see one region from this man's prostate has about 350 and others only have a few tens of copy number aberrations. The same is true for any characteristic that we look of the tumor.
Of course, the obvious question you might ask is, "Is this clinically relevant?
Does it matter?" Slide 38
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Again, a fairly complicated plot, and I'll blow up this area focusing on cancer‐related genes. This plot here is actually focusing on a small set of genes that are particularly clinically relevant. The green squares in PIK3CA are identifying non‐synonymous point mutations, actionable point mutations from sequencing that might tell you this patient might be amenable to mTOR inhibition.
By contrast, the blue dots are pointing out copy number aberrations and you
can see in four regions of this man's prostate, he has deletions of BRCA1, which is commonly associated with germline or familial prostate cancer for completely separate regions of p53 deletions.
And when we superimpose upon this the clinical information about the
disease, you can see that it turns out that the BRCA1 regions are the most aggressive and the potentially targetable PIK3CA ones are not. So that gives a sense of just how much heterogeneity there is in an individual tumor.
Slide 39 Now, this affects copy number markers as well very substantially and we're
looking here at biomarkers that might predict a response. You can see in any individual man, there's heterogeneity in the deletions of p53 or NKX3‐1 or CDH1 suggesting that a biomarker needs to be able to address this type of concern.
Slide 40 Now, to the extreme extent that we observed here, we found multi‐clonality
in a couple of patients. Here is an individual, four regions from his tumor and the top panel is showing copy number aberrations. What you can see is the two regions, the tumor have striking deletions in Chromosome 8 and Chromosome 16. Two other regions have deletions in Chromosome 19. They don't share anything in common.
Similarly, at the point mutation level at the bottom, we can see clearly that
there is no point mutation share between these two regions. In short, the man has two completely genetically distinct tumors within his prostate.
Slide 41 And so, that suggests that there's a real importance to developing
biomarkers based on biopsy specimens, based on what will be used to diagnose the tumor so that we can optimize treatment selection before the tumor actually is resected.
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Slide 42 And so, working with Rob Bristow and a brilliant PhD student co‐supervised
by Rob and myself, we started to take a look at how you might use copy number assays to do so.
Slide 43 We chose a very unique cohort of 126 radiotherapy patients where we had
pre‐radiotherapy biopsies frozen for analysis, and then we validated it on surgery patients. Again, we subjected each of these to copy number profiling and used them to try to asses biomarkers.
Slide 44 We see that the common genes themselves are altered, so you see here
about 40 patients with MYC amplification and that itself serves as a weak biomarker. On the other hand, these only account for a fraction of the patients and they're not very strong biomarkers, so we need much more powerful trends to be able to actually make this clinically useful.
Slide 45 So what Emilie did is start with an unsupervised analysis. She began by
creating a novel clustering technique identifying groups of patients that she could then validate and eventually associate with clinical outcome.
Slide 46 When she did so, she identified four clusters shown by the bright yellow,
green, purple, and red bars on the right side of the plot. Those clusters turned out to have quite distinctive genomic profiles.
Slide 47 For example, Cluster 1 has a characteristic amplification of Chromosome 7.
Cluster 3 has a characteristic deletion on Chromosome 8 and a deletion on Chromosome 16.
Slide 48 When we looked at the outcome of these patients, you would immediately
see that the red cluster has very good outcome relative to the other three.
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And this red cluster, if we go back to the profile plot, is the one with very few alterations.
Slide 47 That made us hypothesize that perhaps it wasn't the individual genes that
were important, but the level of genomic instability. Slide 49 So Emilie developed PGA or the proportion of the genome altered as a proxy
for genomic instability, and that turns out to be a wonderful biomarker. Slide 50 By itself, just knowing the copy number profile allows us to make clinically
useful predictions. Slide 51 She then said, "Maybe I can incorporate this and use both gene‐specific and
general genomic instability information in my biomarker." [0:20:04] So what she did was develop a machine learning technique that would
maximize the number of genes in a signature instead of try to minimize it. She used standard machine learning techniques on that data set, used cross‐validation to try to optimize it, and then would validate it in her independent cohort.
Slide 52 When she did so, it resulted in a truly remarkable classifier, one that has
about 80% accuracy, which you might consider the boundary for clinical utility, and a hazard ratio showing relative risk between the two groups of about six even after adjusting for other clinical criteria.
Slide 53 This signature turns out to work better than any of the RNA signatures that
have been performed to date. We did a heads up comparison on an independent cohort of the predictive ability and significantly better than the blue clinical signature, which is the area under the raw curve of 0.6.
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Slide 54 Very interestingly, when we took a look at this, we were able to identify that
many of the genes that were important were on Chromosome 8. In fact, it turned out that while many people in the field had assumed that there is the deletion of NKX3‐1 and the amplification of MYC that mattered on Chromosome 8, rather there is a large number of features that carry independent prognostic capability and those genes turned out to have interesting biology.
Slide 55 Just a simple example, the copy number alterations in a gene called SBF1 are
also associated with methylation and mRNA abundance differences. Slide 56 And in fact, it goes in exactly the direction you might expect. Here is a gene
that shows enhanced mRNA levels that are associated with good outcomes, so it's a tumor suppressor. It's deleted in prostate cancer and it's hypermethylated in the subset of patients as well.
Slide 57 So what I hope I showed you is that copy number base biomarkers can teach
us a lot about the internal heterogeneity of prostate cancer. In fact, we can even identify that it's potentially multi‐clonal. That highlights the importance of using CNAs as a biomarker from diagnostic material from small amounts of FFPE samples.
Slide 58 I spent most of my time saying "we". We, of course, is a large group of
people who are involved in CPC‐GENE. I mentioned Rob, Theo, John, and Emilie at the beginning. And of course, I'd like to thank all of the other members of my lab. Now, I'll turn it over to Ajay.
Sean Sanders: Thanks so much, Dr. Boutros. Slide 59 We're all going to move right on to our next speaker and that is Dr. Ajay
Pandita.
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Slide 60 Dr. Pandita has over 20 years of experience in the field of molecular
cytogenetics and molecular biology. He previously worked as a scientist for Genentech where he was responsible for developing personalized health care strategies for Genentech molecules in their pipeline.
In 2011, he moved to OncoMDx (recently renamed Core Diagnostics) where
he presently serves as chief science officer. In this position, Dr. Pandita is responsible for developing personalized strategies for projects from early research and preclinical studies and for generating novel biomarker assays for their clinical labs.
A very warm welcome to you, Dr. Pandita. Dr. Ajay Pandita: Thanks, Sean, for the kind introduction and also for the opportunity to
present here. I'll try to continue from where Paul left, and Paul showed how greatly in the lab you could do a lot of work and find signatures or markers that could be used ultimately for the best management or clinical management for the patients.
I'll give an example of something that we use in a Phase 2 trial that was
published earlier this year, which basically enhances the point of taking it from the bench to the bed, but also in the initial study that we published late last year where we were trying to get information from what happened in the patients and trying to see how can we bring that back to the lab to understand how again to look for markers or ways in which we can provide management to patients at the best possible way we can.
Slide 61 Chromosomal alterations or aberrations that lead to copy number changes
are a hallmark for a cancer cell. I begin by showing a normal karyotype where you see on your left hand side a routine G‐banded image of the chromosomes, which has been really helpful especially in liquid tumors where actively mitotic cells can grow and we can look at the alterations that are present, and define whether you stratified the patients really well in terms of how they would do and if there are any treatments that quickly can be targeted towards that.
However, with the advent of molecular biology, we try to infuse some color
into our black and white world of G‐banding and using FISH, which is more amenable to solid tumors. We could also look into what's happening on a cell
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to cell basis for the known genes, and specifically, it has been really helpful in solid tumors.
The image that you see towards your right is a normal FISH pattern in a cell
for a gene that's a locus‐specific gene. In this case, it's p10; that's in red color, and the control centromeric probe that is for Chromosome 10 that you see in the green color.
[0:25:02] Slide 62 However, when you go to a cancer patient's karyotype ‐‐ and this is
something that you see that there could be changes that could vary, specifically this one ‐‐ to illustrate my point of how many changes can happen, it was really tough to illustrate that in a normal G‐banded or a G‐banded image.
So what you see over here is spectral karyotype where each chromosome
has its distinct color. Wherever you see a deviation, that means there's some kind of a rearrangement or aberration that's happening on the chromosome. And as you can see, there are multiple copies of the chromosomes, unusual chromosomes, and also the rearrangements.
Ultimately, there were a lot of losses and gains that happened in this patient
due to these alterations. Again, this can also be seen ‐‐ I don't know whether you can see it properly or not, but this can also be seen using the FISH analysis. In this case, this is a HER2 FISH status performed on a patient sample where there are multiple copy gains, where there are low copy gains, and where you could see three to four red signals in the individual nuclei, which can range from being highly amplified where you see in the bottom panel ‐‐ where you could see there at least 50 to 60 copies of HER2 in comparison to two to three copies of the control gene.
Slide 63 However, that said, it always doesn't have to be as complex as that. Even a
small change of extra chromosome or tiny Chromosome 21 in Down syndrome, which you can see in this G‐banded image, also is a bit ‐‐ a number of developmental disability and significantly reduced life span of the patient. So it could be a small change as a mutation, a single chromosome gain, or a single loci or gene gain to highly amplified and polyploid genomes that could cause changes into the patient taking it from a normal cell to a cancer cell.
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Slide 64 Structure and numerical changes are, as I said, a hallmark for the cancer
genome. What we have here is the multiple ways in which these aberrations can affect a cell where it could be either changes in the individual chromosomes or you could see changes in the whole genome. Going from a diploid, it could be a triploid, tetraploid and so on.
More interestingly also, there could be low level and high level gains, which
is gene amplification that has been started for a while and have been one of the first alterations in terms of copy number changes that have been studied vastly and used as a factor especially in breast cancer patients where the HER2 amplified patients have a drug especially targeting against it.
I won't talk about the structure changes here, but they have also been shown
to be quite important, and one of the recent examples has been the ALK translocation in lung cancer where it's a highly specific drug against the alteration has been very fruitful in the management of the patients.
Slide 65 As we know, for the last many years, a lot of focus has been documented
towards the accumulation of genetic events, be it epigenetic mutations or copy number structural changes that lead to a cancer cell. A lot of interest currently in the community has been to identify and understand the contributions that these alterations have towards the progression or the biology of the tumor.
However, in recent years, a lot of interest has been towards to see whether
we can understand these changes a bit better and use drugs against it to benefit the patient ultimately where you would see that there would be a cohort of patients where the diagnostic positive and the diagnostic negative patients would show difference in their prognosis, but then ultimately, if there's a drug that specifically targeted against it, the patient that would have the alteration gain the maximum benefit of the drug.
Slide 66 However, this is not a very new concept. This is a concept that was put
forward in the early 1900s by Boveri where he did mention on his experiments on sea urchin eggs that they are growth‐inhibiting and promoting chromosomes that result in unlimited multiplication.
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I think that's where I would think the basis is of looking at these abnormal conditions in the chromosomes and apply it until we had technologies ultimately where we could record and document these changes and associate it with different cancers and what they do on cancers.
Slide 67 However, with the completion of the human genome project, it has greatly
made a big difference in terms of the data that's available and very nicely covered by Paul, that you could see that you could look at different regions of the genomes, abnormalities of the genomes with new technologies that are upcoming each and every day where you can look into the stratifications of these signatures that were supposed to be for smaller portions of the genome. However, one of the challenges is how do we incorporate it into our diagnosis or the diagnostic world.
[0:30:04] Slide 68 Until now, pathologists have done a great job in identifying and diagnosing
the cancers, and also in helping in mapping and reading the tumors. However, one of the limitations ‐‐
Slide 69 Before that, this is just an H&E Slide of which the majority of Pathology works
off of where they use it to diagnose, and this is a case of a prostate cancer. Whenever there are little bit challenges, they do have markers in terms of
protein expressions that do help identify and confirm the diagnosis in case there are difference of opinions in what the final diagnosis is.
Slide 70 However, one of the limitations in pathology, conventional pathology, is that
sometimes it's really difficult to diagnose rare tumors, but at the same time, it's really hard to predict which are the good or bad tumors, also, if a particular tumor would be more sensitive to one type of treatment as compared to the other.
Slide 71
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I think that's where biomarkers have played a great role in trying to help the pathologist as an additional tool to help stratify these patients where we can make those decisions and help make those decisions on this patient.
Again, I go back to what Paul illustrated where you see low risks, high risks,
and the intermediate type, and then you can tailor your treatment based on that whether you want to go more aggressive or with indolent tumors where you want to wait and watch and be actively surveilling the tumors to see what's happening.
Again, biomarkers are the ‐‐ every time, I guess, you have to create a term for
anything that you use, biomarker is one of such things. It's basically just a marker that you use to measure any biological process. Even though you may not think about it, even high blood pressure is a biomarker for increased risk of stroke, so you can take it to something as simple as that.
Slide 72 However, through the years, the biomarkers have also evolved quite a bit
starting from something that was quite helpful in terms of making the appropriate diagnosis for the patients.
Second in line came more about the prognosis where they could ‐‐ and I
think it's more relevant now where we do manage to identify tumors early on, and at that stage, there's a lot of talk about overdiagnosis and overtreatment. These markers definitely can help the clinicians to make those strategies that would be ultimately beneficial to the patient.
The most exciting part, I think, in these days is the predictive biomarkers
where a lot companies and a lot of studies and a lot of work is being done towards matching the patient to a particular drug. As we know, all these drugs have side effects and we want to minimize it and maximize the effect of the drug, and selecting for that group of patients always is helpful in making that.
This is something that I think is becoming much more interesting more
recently, is looking into the resistant markers. This was something that we're seeing more and more regarded in therapy, but there is resistance that's developing after a period of time. This is something where a lot of work now is started being done for patients where we do see that there are targeted therapies against them, how can we look for these markers, can we know them upfront, and can we have drugs tailored that would try to combat or treat the patients much better.
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Slide 73 Just to reiterate that prognostic value of biomarkers, as I was mentioning, is
that especially these days, since we do diagnose these patients quite early and with a lot of talk about overdiagnosis and overtreatment, these biomarkers do help in deciding how to go ahead with the patient in terms of its indolent tumor or progressive tumor.
Slide 74 This is a classic example of HER2 gene amplification being used as a
prognostic factor in breast cancer. You can see the dotted line where the patients with HER2 amplifications do much worse than the patients that are not amplified for the gene.
Slide 75 Inclusive of that, there are many other prognostic markers that have been
used. P10 has been used for prostate cancer. MET has been used for lung cancer. There were a lot of studies, and anyone who just attended the recent ASCO Conference would have seen that there's a lot of work that's being put towards both the companion diagnostic of predictive biomarkers and prognostic biomarkers in terms of patient stratification for clinical therapies.
The exciting part again being predictive biomarkers where the companion
diagnostic ‐‐ and I've listed some examples here where you could clearly see that it does create a benefit and can go forward in the top without showing one of the poster children for solitary which was the HER2 amplification and the use of the drug trastuzumab.
Slide 76 And what you see in the plot, a couple of plots right now, is that there was
basically no difference between the patients who did receive the drug with the patients who were not stratified by it.
[0:35:08] But once we started stratifying the patients and looking into which of the
ones were HER2 positive and negative, you could see that the patients do stratify quite nicely where the patient that did receive the drug and have the amplification did much better than the patients that did not.
Slide 77
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This is just a list and obviously by no means a complete list. It seems to be
changing and being updated every other month, but there is a lot of focus to what's right now using biomarkers and matching the drugs to it to the effect that a lot of the biotech companies now or biopharma companies are using it in their clinical development pipeline where initially it was like this and just the TMN staging are just based on the pathology and going through the process of the drug development.
Slide 79 However, now ‐‐ even though I won't go into the details of it ‐‐ biomarkers do
play an important role throughout the role in the drug development with ultimately a companion diagnostic being launched with the drug wherever is possible. One of the recent examples as I've mentioned was ALK in lung cancers, but there was a lot of excitement at ASCO and a lot of new areas where biomarkers are being used for these purposes.
Slide 80 I'll take you to a study by the Phase 2 trial that was done and published early
this year in non‐small cell lung cancer where I was a part of it being at Genentech at the time.
Basically, what it was is that looking at the MET overexpression, and there
was a lot of underlying evidence based on ‐‐ Slide 81 ‐‐ the genetics, the pre‐clinical work, the transgenic model, and also more
importantly, that MET has been shown to be a really great prognostic factor in lung cancer patients where the patients that do have the MET overexpression or amplification do worse than the patients that do not.
Slide 82 On the same line, you could see that from a drug company standpoint, you
could see that there are a lot of alterations in MET that are observed across the board. In multiple tumor types, it does make it an interesting proposition to start a drug development program in the area.
However, one of the challenges at the time was how to come up with a
diagnostic and one of the best diagnostics for it.
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Slide 83 Something unique that was done in this study is that we tried to look at
multiple assays, at the same time looking for the same alteration via IHC, FISH, mRNA expression, HGF and plasma levels of it. The aim was that ultimately, we can find the best ‐‐ ultimately, once we have all the data, we could find the best diagnostic that would select for the patients.
And what they could see and understand that if the pathway is completely
turned on, truly turned on, and if you look at those alterations at multiple levels, it gives you much more confidence in what's happening to the patient.
Slide 84 Again, just the diagnostic strategy, as I said, we went with multiple
alterations, multiple tests, but the focus was looking towards IHC where we went through the process ‐‐ and I won't show it over here ‐‐ a lengthy process of looking at IHC and coming up with the cutoffs and everything else.
Similarly for the FISH assay, looking at the copy number changes based on
the published literature from Dr. Garcia's group from the University of Colorado and doing some in‐house studies. We did see how we could best have the cutoffs for these patients.
Slide 85 What was quite interesting is that in the Phase 2 study that we could see ‐‐
and this is the station stratification that was based on IHC, MET IHC, and the blue line is the patient that did get a combination of erlotinib, which is against EGFR, again, a common change in lung cancer patients.
So patients that did receive both an anti‐MET therapy and erlotinib did much
better compared to the patient that did not, and we did see the hazard ratios and the range of 0.5 for the PFS and around 0.37 for overall survival, which was quite exciting to see in a small group of 120‐odd patients.
Slide 86 We did also look at other biomarkers that we had in the exploratory assay
and we did see that FISH also very nicely predicted and showed that the benefit that was provided to the patient that did receive the anti‐MET therapy along with erlotinib did much better compared to the patients that did not.
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However, the hazard ratios were not as good and the numbers, obviously because of the numbers of patients that were selected under each category, under each analyte were different, so the significance of it also changed according to that.
However, for the other markers based on the numbers or anything else, we
just could not see that they really helped in the stratification of the patient. [0:40:05] In any, we do show that there was a select group that would get any benefit
from those drugs. So in hindsight, it was kind of nice that we had a chance to go through all of this and understand what was happening and use the best appropriate test moving forward in the Phase 3 trial to see what happens to the patient.
Slide 87 In this case obviously, it was potent and selected toward that IHC and FISH
were independent predictors. As I mentioned, we went ahead with IHC into the Phase 3 to do that.
Slide 89 Going into the second part where I was talking more about the resistant
biomarkers ‐‐ and this was a recent study that we finished towards the end of last year and published towards the end of last year ‐‐ is that in a lot of targeted therapies now, we're seeing a lot of resistance on these patients coming in.
It would be nice to look and understand these alterations or these resistant
biomarkers or mechanisms upfront so that we could help the patients at the time when these patients stop responding to the drug, or if possible, the mechanism or the biological means to look at them even upfront to see whether there are population of cells that do have them.
Slide 88 Some of the good examples for resistant biomarkers have been studied,
which has shown that the mutations in the abl‐kinase domain of imatinib or more classically, the T790M in anti‐EGFR therapy.
Slide 90
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So based on that, we went ahead and tried to see what we could do for the PI3K starter where a lot of trials currently are being done and to understand whether there are many mechanisms that we could look for.
So we took cell lines that were HER2 positive and had the mutation of PIK3CA
and that were anti‐PI3K inhibitors. We developed resistance in these cell lines to these inhibitors and went on to study what the alterations would be. This is where using the new technology from Affymetrix came in quite handy and this technology of looking at copy number changes is based on molecular inversion probes. I've listed the website there that you can get more details about the technology and how it works.
Slide 91 But what was interesting to us is that when we looked at the plot, to our
surprise, we saw that PIK3CA itself was highly amplified, which was not the case in the original parental tumor line.
To further confirm and it's something similar to what Paul mentioned is that
initially since we were surprised, we just wanted to make sure that we were reading it correctly, and what we could see quite nicely is that in the parental line, even though there were six copies of the low copy number gains, there was nothing as amplified as you can see on the right hand side where one of the mutant cell lines, KPL‐4PR.5 where there are multiple copies on the range of at least 30 to 50 copies of PIK3CA, which are presented as red bars on the chromosomes where the arrows are.
So this was something really new especially in the PI3K pathway that hadn't
been shown before. The amplification of the mutant gene itself did make a difference.
Slide 92 However, to confirm whether it really meant anything biologically, we did go
ahead and then used siRNAs to knock down the expression of the PI3 100 alpha unit and try to see whether we could bring back the sensitivity of these cell lines, these resistant cell lines to the drug to what it was for the parental cell lines.
In the graph over here, you could see the red and blue lines and you could
see that the amplified resistant lines, once they were knocked down, the expression of PIK3CA was knocked down, you could see that the levels of inhibition were almost the same as they were in the parental lines.
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It's quite exciting that we could use the technologies to find novel mechanisms of that resistance especially in PIK3CA and try to take it into patient samples more and try to see whether these would be the means of looking into alterations.
Slide 93 Basically, what I wanted to take forward from what Paul said is that the one
part in the lab is to look for these signatures and biomarkers that would be a good use to stratify these patients, and I believe there are new technologies to provide us a lot of means in doing that and ultimately being used in where it ultimately matters the most in the patients where we could stratify the patients and see how best can they be clinically managed in terms of prognosis and prediction and drug response to the drugs that are given to them.
Slide 94 Ultimately, where it would be helpful is that ‐‐ this cartoon is just to show
that there's a lot of heterogeneity that happens in terms of sensitivity to drugs or similar drugs, and the biomarkers would be something that I hope going forward is going to be able and we are seeing that it is doing it, but kind of take it forward and see how we can segregate these different groups and where we can know which drug is going to be effective, where to go for active therapy or aggressive therapy, where do we wait and watch, and which drugs would be best suited for the patient with the least toxic effects.
[0:45:18] Slide 95 So with that, I end it and acknowledge again a lot of people who were
involved in these groups being in the Phase 2 trial. A lot of this work was done when I was at Genentech, but definitely foremost, thanks to the patients and the families of the patients that do provide the tumor for the studies and go through the process where we can make these discoveries and try to understand how best to then ultimately provide them the best clinical management we can. Thank you.
Sean Sanders: Fantastic! Thank you so much, Dr. Pandita. Thank you also to Dr. Boutros for
the very engaging presentation. We're going to move quickly along to some questions a bit of our online viewers.
Slide 96
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Now, we just have a few minutes left on the webinar, but we might run a
couple of minutes over time so we can squeeze in some questions, and I hope our audience will stay with us.
A reminder, too, if you're watching us live that you can still submit your
questions by typing them into the text box and clicking the submit button. If you don't see that box, just click the red Q&A icon and it should appear.
Dr. Boutros, I'm going to give you the first question, and that is, is it
important to complement seeing the analysis studies with gene expression analysis and why might that be?
Dr. Paul Boutros: That's a great question. I think it's absolutely valuable to do so. By doing that
complementation, you're able to really identify potential pathways or mechanisms of the copy number aberrations that you see. You can also identify the dysregulation of a gene that's not always present at the copy number level.
For example, SPF1 we showed is also changed at the methylation level, but
has the same kind of consequence, so I think it's absolutely very valuable to do so.
Sean Sanders: Great! Dr. Pandita, anything to add to that? Dr. Ajay Pandita: I would just like to further really quick what Paul just mentioned that
definitely yes, that's what I had just shown in the Phase 2 study that we did. In fact, we did look at multiple levels of alterations that can be detected for a gene or a pathway as it gives a better sense of when is the pathway truly being turned on or off and getting us a better handle of where do the patient benefit most by a given drug and understanding how to move forward.
Sean Sanders: Great! And coming back to you, Dr. Boutros, in your studies, how much
genomic DNA was extracted from your biopsies? The viewer is also asking what platform for array CGH you're using.
Dr. Paul Boutros: Good question. The majority if our biopsy specimens, we were extracting
anywhere between about 10 nanograms and 200 nanograms, and the majority of our arrays were done with 14 nanograms of material. Some were actually done with smaller amounts of material and I think the smallest that we used was something like 10 or 15 nanograms of input. Of course, as I'm sure most people know, how you quantitate input DNA is tricky and we were using a cubit for quantitation, so that might put into perspective just how small those amounts are.
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For the platform, we standardized this independent of whether the sample
was FFPE or large volume or small volume. And so, we used OncoScan arrays for everything that we did and some of the data that I showed you was the version two of the OncoScan and some was version three.
Sean Sanders: Great! Let me stay with you, Dr. Boutros, for the next question. This viewer
asks whether the variation of mutation frequency that you seek could be a function of the percentage of tumor being analyzed.
Dr. Paul Boutros: Yeah. We thought about that a long time, so a couple of things. One is that
we were microdissecting these regions so they are inherently much pure than most you would see. And in addition, by estimation by pathologists, we would get tumor nuclei percentages around 80% to 85%, but we independently validated that computationally using both the sequencing data and using the array data.
In each case, they confirm that it's about 80% to 90% tumor cellular, so we
actually don't think we had a contamination issue at all. That being said, some of the differences are just so large that it's almost impossible. We've got amplifications of several hundredfold in one region and it's not present at all in another, so we should've been robust to see that even if there were fairly acellular tumors, I think, so I don't think that's a major concern for the study.
Sean Sanders: Dr. Pandita, let me come to you. Have you seen if copy number change
detected in FFPE samples can be reproduced from fresh frozen tissue from the same biopsy?
[0:50:04] Dr. Ajay Pandita: That's a good question. I think we get a lot of those comments from time to
time as whether it can be done on fresh frozen. The point I would make is that it can be done, but how reproducible it is sometimes becomes very tough. One of the major problems we have is that one tends to lose the architecture of the tissue at the same time.
So to kind of see the nucleic quite compact and the way we see it in FFPE
tissues, sometimes it becomes very tough to diagnose. For that reason, the preference is generally given towards FFPE tissues, but as I've said, even though not reproducible, we have managed to get it working on frozen tissues.
Sean Sanders: All right. Dr. Boutros, anything to add to that?
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Dr. Paul Boutros: No, I completely agree with that. There are some clear advantages for frozen
for some things and FFPE for others. Sean Sanders: Here's another question in the same vein whether CNVs can be detected in
circulating tumor cells. Have you looked at that, Dr. Boutros? Dr. Paul Boutros: Yeah. We're trying that exact assay right now. Unfortunately or fortunately,
we work largely in localize prostate cancer and these patients don't generally have a large number of CTCs. We have been successful doing it from circulating DNA, so not from the cells themselves, but from DNA that's found in the plasma.
We published on that a couple of years ago and we actually found some
interesting profiles of it, so at least it's technically possible, but whether or not it's clinically useful for these patients, that I'm not sure.
Sean Sanders: All right. Dr. Pandita, have you got any experiences with CTCs? Dr. Ajay Pandita: Yes. We have from the point of view of FISH for detecting copy number
changes, I think it's very well‐established in HER2 cancer and even in prostate cancer. There have been studies to show it and we've also done it.
However, the challenging part for CTCs only come through the platform
we're using to enrich the cells where how eminent they are for the downstream analysis, if they can be easily harvested and put on a slide where they're preserved and you could still maintain that you're looking at the CTCs and not the confounding other cell types in there, then definitely it can be useful. It has its challenges, but it can.
Sean Sanders: Excellent! Dr. Boutros, back to you, can you explain how you differentiate
focal amplification and regular copy number gain based on your microarray data?
Dr. Paul Boutros: Yes, so this is something that I confess that we hadn't really expected to be
able to do, but the array platform that we use actually does it really robustly. Basically, it all comes down to the reproducibility probe to probe and the spacing of probes and the arrays that we're using of several hundred thousand probes. That means that you already would have reasonable confidence, but very importantly, I guess they designed it so that there are more probes around oncogenes and around key genic regions.
As an example, if you compare the classic SNP‐6 or other genotyping arrays,
their probe density in the region that we found that really interesting focal
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amplification on was actually not particularly high and you would've missed it. Actually, other studies have missed it.
By contrast, having a bit higher probe density, that really helps and you can
pick these things out quite quickly just because the signal is robust and you've got a good probe density, so yeah, it turns out to be bioinformatically very straightforward.
Sean Sanders: All right. Dr. Pandita, I'm going to come to you with maybe a similar question.
You said that whole genome technologies provide contextual information, in other words, the ability to distinguish focal from broader events. For example, focal MET amplification versus the amplification of the entire chromosome. Is this information informative especially for the clinic?
Dr. Ajay Pandita: I think there were studies that have been shown in terms of ‐‐ I think it's
more shown in the deletions rather than in the gains or amplifications where how the large the deletion is does have an impact on how well the patient does or not. However, on the other part, if we're looking at it being used as a predictive marker, in terms of your drug, it could start it against a specific gene.
In that case, what really matters is whether that gene is being overexpressed
or altered and not so much what's happening on the rest of the part of the genome. However, that may either as a passenger or even biologically co‐amplify other genes that may make an effect there, but in general, if you're looking at targeted directly, then you're pretty much looking at what the target is and looking at whether that's being overexpressed or amplified or altered.
Sean Sanders: Dr. Boutros, I'm going to come to you with one final question. What is the
degree of CNV that you observe in non‐tumor cells in the patients that you look at?
[0:55:05] Dr. Paul Boutros: That's a very good question. We did not do direct profiling of tumor‐adjacent
normals. I know that there are several groups that have done that type of study and I believe those manuscripts are now in submission, so I think the community will find out shortly. I'm very curious about what that would look like as well.
What we used as normal controls was blood, and in the blood, of course we
see very few CNVs concordant with the germline analyses from Steve Share's
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group and other groups, but in tumor‐adjacent normal tissue, that's an open question in prostate cancer that's going to be very fascinating.
Sean Sanders: Great! Well, we are unfortunately out of time for our webinar today. I just
want to say a big "thank you" to our speakers, Dr. Paul Boutros from the Ontario Institute for Cancer Research and Dr. Ajay Pandita from Core Diagnostics for being on the line with us today and for their very interesting talks and discussion.
Many thanks to our online audience for the questions you submitted to the
panel. Sorry that we didn't have time to get through all of them. Please go to the URL now at the bottom of your slide view to learn more about resources related to today's discussion and look out for more webinars from Science available at webinar.sciencemag.org.
Slide 97 This particular webinar will be made available to you again as an on‐demand
presentation within about 48 hours from now. We'd also love to hear what you thought of the webinar. Send us an email at the address now up in your slide viewer, [email protected].
Again, thank you very much to our panel and to Affymetrix for their kind
sponsorship of today's educational seminar. Goodbye. [0:56:43] End of Audio