Gene Expression and Retinoblastoma“Cancer of the Eye”

Wen Jie Zhang, MD, PhD

School of Medicine, Health Sciences and EngineeringSusquehanna Township High School

Lecture Series Week 9, September 2013

Clinical Relevance of This Week’s Topic

Eyes that look at the world

Eyes that guard our homes

Eyes that work at night

Eyes that look at us on Halloween

Eyes that can talk

Eyes that look at the future

Eyes that may lose vision

Retinoblastoma, Rb

Anatomy of the Eye

Retinoblastoma (Rb)Cancer of the Eye

• Rapid developing cancer of the childhood– Outgrowth of immature cells of the Retina, the

light-detecting tissue in the eye• Diagnosed:

90% of Rb within the first 3 years of agethe remaining within the 6 years of age

Very rare after 6 years of age• Incidence of 18,000 to 30,000 live births worldwide

Retinoblastoma (Rb)Categories (Types)

• Familial RbHereditary and bilateral (affects both eyes)Approx 10%

• Sporadic RbNon-hereditary and unilateral (affects one eye)Approx 70%

Retinoblastoma (Rb)Signs

• Leukocoria (white pupil, 60% of Rb)

Retinoblastoma (Rb) Signs

• Strabismus (squint, cross-eye, 20% of Rb)

Retinoblastoma (Rb) Signs

• Other signs (10% of Rb)– Eye swelling with pain and redness

Funduscopic finding of a retinoblastoma

Funduscopic findingof a retinoblastoma

Migration of retinoblastoma “seeds“ onto the iris surface.

A Drawing of RetinoblastomaJ. Wardrop, 1809

A Surgically Removed Retinoblastoma

Mechanism(s) of Retinoblastoma

CarcinogenesisEnvironmental Factors Genetic Factors

Physical

Chemical

Biological

(Mutations)

Substitutions

Deletions

Insertions

Lifestyle

Cancer(Carcinogens)

Translocations

Tumor Suppressor GenesGene Human Disease Function

APC Colon cancer Interacts with cateninsDCC Colon cancer CAM domainsE-cadherin Breast cancer Intracellularly interacts(CDH1) with cateninsDPC4 Pancreatic cancer TGF--related signalingBRCA1 Mammary cancer/ DNA damage repair,

Ovarian cancer checkpoint control, apoptosisBRCA2 Mammary cancer DNA damage repair, genomic

stabilityATM Ataxia-telangiectasia DNA damage response

mutated gene upstream in p53 pathwayP53 Mutated in >50% Transcription factor,

tumors checkpoint control, apoptosis

Mechanism(s) of Retinoblastoma

• RB1 gene encodes a protein (pRb) that serves as a tumor suppressor– Suppress cell (division) cycle

• Mutation of RB1 gene – Results a defective pRb protein, therefore,

unable to suppress cell cycle leading uncontrolled cell division (tumor formation)

Cell Division Cycle Under Control

If not controlled,Cancer (tumor)

Formation

RB1 Gene Location

13q14.1-q14.2

RB1 gene

Crystal Structureof Retinoblastoma Protein (pRb)

Crystal Structure of the Retinoblastoma Tumor Suppressor Protein Bound to E2F

Retinoblastoma Protein iscolored blue, E2F is violet

Carcinogenesis – “Two-hit” Hypothesis(Knudson, 1971)

First hit Second hit Outcome

GermlineMutation

(Insertion/Deletion)

First Mutation(Insertion/Deletion)

InheritedBefore birth

Cancerdevelops

Second Mutation(Insertion/Deletion)

AcquiredAfter birth

SomaticGenetic

Multi-stepprocess

“Two-hit” Hypothesis

• Familial Rb fits the hypothesis

First hit: One mutated gene inherited (recessive)

Second hit: Another gene is also mutated due to different reason(s) (e.g., UV radiation, reported in New Zealand)

Common MutationsSubstitutions (point mutation)

In a DNA sequence, a single nucleotide is exchanged for another (A G, C T), leading to missense or nonsense mutation.

Insertions (insertion mutation)The addition of one or more nucleotide base pairs into a DNA sequence.

Deletions (deletion mutation)Part of a chromosome or a sequence (base pairs) of DNA is missing from a DNA sequence.

Genetic Testing

• Several methods for detecting the RB1 gene mutations have been developed

• A method that can detect large deletions in the RB1 gene that correlate with advanced stage retinoblastoma

“Well Baby Screening” for Signs for Early Diagnosis

Treatment• Simple enucleation (removal of the eye)• Eye-sparing radiotherapy• Chemotherapy-based multi-modality therapy

– Laser therapy– Cryotherapy (freezing therapy at −196ºC or

−321ºF) 

Images of Retinoblastoma (Rb) tumorsby Retino-scan before and during chemotherapy

Outcomes

• Rb has one of the best cure rates (95-98%) among all childhood cancers

• 9 out of every 10 patients survive into adulthood

Eyes that look at the future

The Coda