IRAP – January 25, 2021

Presented by

Glass slides are available for all cases except #4.

All cases are available virtually:

https://uchicago.pathpresenter.com/#/public/presentation/display?token=70d44e4f

Link to presentation recording: https://youtu.be/5h-GKxsgTzg

Case #1: Drs Heather Chen-Yost and Aliya N. Husain

Diagnosis: Giant Cell Myocarditis

Clinical History: The patient is a 69-year-old male with a past history of hypothyroidism and hyperlipidemia with a new diagnosis of non-ischemic cardiomyopathy. He had an episode of syncope with cardiac arrest and was transferred to an outside hospital. An ICD was placed but soon after, he had a second episode of cardiac arrest. The patient was successfully revived with CPR, but remained very hypotensive. He was transferred to UCMC for extracorporeal membrane oxygenation (ECMO) and received a heart transplant a week later.

Gross and Microscopic Findings: The explanted heart is enlarged (478 g), somewhat globoid, and has a moderate increase in epicardial fat. The coronary arteries showed mild calcific atherosclerosis. The cut surface is mottled diffusely but does not show distinct infarcts.

Histology shows diffuse infiltration of various inflammatory cells comprised of predominantly multi-nucleated giant cells and followed by monocytes, lymphocytes, and eosinophils. There is myocyte damage surrounded by multi-nucleated giant cells. Granulomas are not observed. The blood vessels are patent without thrombosis.

Differential Diagnosis:

Myocarditiso Giant cello Fulminant lymphocytico Eosinophilic

Granulomatous diseaseo Non-caseating

Giant cell myocarditis Cardiac sarcoidosis

o Caseating granulomas Infectious (TB, fungal, etc)

Ancillary Studies: If there are granulomas, perform an AFB and GMS. Giant cell myocarditis would not show organisms in the granulomas. If curious, one would expect to see many CD68 positive macrophages. For the lymphocytes, there will be more CD3 positive T-cells than CD20 positive B-cells. Of the T-cells, there will be more CD8 positive T-cells than CD4 positive T-cells.

Discussion: Giant cell myocarditis (GCM) is a rare disease that mostly affects young to middle age adults. The patients present with rapid-onset congestive heart failure with symptoms similar to acute myocardial infarction. The etiology of the disease is not fully understood, but the consensus is that this is most likely due to immune dysregulation by T-lymphocytes that lead to autoimmunization of cardiac myosin. There is upregulation of genes involved in the Th1 pathway and an association with autoimmune diseases.

Grossly, the heart is diffusely mottled and discolored. On histology, there will be a diffuse or multi-focal inflammatory infiltrate comprised mostly of multi-nucleated giant cells and T-lymphocytes. Plasma cells and eosinophils are also present. There is prominent myocyte damage. Poorly formed non-necrotizing granulomas can be present. GCM can also be isolated to the ventricles or atria.

The primary item on the differential is cardiac sarcoidosis (CS). Below is a table describing the differences between the two:

Histologic Feature GCM CS

Inflammation Diffuse or multi-focal

Lymphocytes, eosinophils, giant cells

Limited

Lymphocytes, giant cells (usually in center of granulomas)

Myocyte necrosis Present Absent

Granulomas Can have poorly formed non-necrotizing granulomas

More common, better formed, non-necrotizing

Fibrosis Not common More common

GCM is treated with high-dose immunosuppressives and transplant. Without therapy, the onset of death is on average 3 months. GCM can recur in up to 20% of transplanted hearts, but the long-term survival time is not impacted.

References:

1. Avellini, C., G. Alampi, V. Cocchi, M. G. Morritti, O. Leone, E. Sabattini, S. Pileri, and A. Piccaluga. “Acute Idiopathic Interstitial Giant Cell Myocarditis. A Histological and Immunohistological Study of a Case.” Pathologica 83, no. 1084 (April 1991): 229–35.

2. Blauwet, Lori A., and Leslie T. Cooper. “Idiopathic Giant Cell Myocarditis and Cardiac Sarcoidosis.” Heart Failure Reviews 18, no. 6 (November 2013): 733–46.

3. Cooper, Leslie T., Gerald J. Berry, and Ralph Shabetai. “Idiopathic Giant-Cell Myocarditis — Natural History and Treatment.” New England Journal of Medicine 336, no. 26 (June 26, 1997): 1860–66.

4. Larsen, Brandon T., Joseph J. Maleszewski, William D. Edwards, Leslie T. Cooper, Richard E. Sobonya, V. Eric Thompson, Simon G. Duckett, Charles R. Peebles, Iain A. Simpson, and Henry D. Tazelaar. “Atrial Giant Cell Myocarditis: A Distinctive Clinicopathologic Entity.” Circulation 127, no. 1 (January 2013): 39–47.

5. Luk, Adriana. “Recurrent Cardiac Amyloidosis Following Previous Heart Transplantation.” Cardiovascular Pathology, 2010, 5.

6. Okura, Yuji, G. William Dec, Joshua M Hare, Makoto Kodama, Gerald J Berry, Henry D Tazelaar, Kent R Bailey, and Leslie T Cooper. “A Clinical and Histopathologic Comparison of Cardiac Sarcoidosis and Idiopathic Giant Cell Myocarditis.” Journal of the American College of Cardiology 41, no. 2 (January 15, 2003): 322–29.

7. Rosenbaum, Andrew N., and Brooks S. Edwards. “Current Indications, Strategies, and Outcomes with Cardiac Transplantation for Cardiac Amyloidosis and Sarcoidosis:” Current Opinion in Organ Transplantation 20, no. 5 (October 2015): 584–92.

8. Scott, Robert L., Norman B. Ratliff, Randall C. Starling, and James B. Young. “Recurrence of Giant Cell Myocarditis in Cardiac Allograft.” The Journal of Heart and Lung Transplantation 20, no. 3 (March 1, 2001): 375–80.

9. Sun, Yang, Hong Zhao, Laifeng Song, Qingzhi Wang, Yan Chu, Jie Huang, and Shengshou Hu. “[Histological and ultrastructural features of giant cell myocarditis: report of 3 cases].” Zhonghua Bing Li Xue Za Zhi = Chinese Journal of Pathology 44, no. 2 (February 2015): 123–27.

10. Xu, Jin, and Erin G. Brooks. “Giant Cell Myocarditis: A Brief Review.” Archives of Pathology & Laboratory Medicine 140, no. 12 (December 1, 2016): 1429–34.

Case #2: Drs. Kristina Doytcheva and Jennifer Bennett

Diagnosis: Fumarate Hydratase Deficient Uterine Leiomyomas

Clinical History: The patient is a 32-year-old G7P7007 female with a history of symptomatic uterine fibroids who presented for a total abdominal hysterectomy and bilateral salpingectomy. CT upper abdomen and pelvis revealed an enlarged uterus, 17.1 cm in greatest dimension, with hyper-vascular lesions likely representing fibroids.

Gross and Microscopic Findings: Gross examination revealed multiple well-defined, white, whorled myometrial nodules ranging from 2.3 to 8.0 cm. Microscopically, a cellular smooth muscle tumor with an

alveolar pattern of edema, staghorn blood vessels, and hyperchromatic bizarre nuclei was observed. On high-power examination, eosinophilic cytoplasmic globules and prominent macronucleoli with perinucleolar halos were noted. Necrosis and mitoses were not appreciated.

Differential Diagnosis:

Leiomyosarcoma Smooth muscle tumor of uncertain potential (STUMP) Leiomyoma variants

o Hydropic Leiomyomao Leiomyoma with Bizarre Nucleio Fumarate Hydratase Deficient (FH-d) Leiomyoma

Ancillary Studies:

IHC: Fumarate hydratase stain negative in all tumor cells Molecular testing:

o Germline testing: FH Variant of Uncertain Significance: c.1053G>A (p.Gly352Asp)o Somatic testing: No additional FH mutations or copy number changes were identified

Discussion: Uterine leiomyomas are the most common tumor of the female reproductive tract and pose a considerable health burden in the female population. Fumarate hydratase deficient (FH-d) leiomyomas are characterized by staghorn blood vessels, an alveolar pattern of edema, eosinophilic cytoplasmic globules, and prominent macronuclei with perinuclear halos. Bizarre nuclei may be present. FH immunohistochemical stain is often negative in the tumor cells, but a caveat exists as in some patients with a missense FH mutation, a non-functioning protein may be produced that is still detected by the immunostain. Therefore, complete loss of FH is helpful in the diagnosis, while retained expression does not exclude the entity.

FH is essential in the Krebs cycle as it converts fumarate to malate. If either a somatic or germline FH mutation is present, fumarate accumulates in the cell and exerts downstream effects such as succination of cysteine residues on proteins and activation of hypoxia inducible factor 1 (HIF-1). FH-d leiomyomas have been reported in up to 1.6% of all leiomyomas and if a germline mutation is present, is a component of the hereditary leiomyomatosis and renal cell carcinoma (HLRCC) syndrome. This syndrome is autosomal dominant and patients are predisposed to the development of cutaneous and uterine leiomyomas, as well as an aggressive form of renal cell carcinoma. Uterine leiomyomas in these patients are diagnosed at an average age of 28 years and most women undergo myomectomy or hysterectomy in their thirties. Approximately 15% of patients develop an aggressive form of renal cell carcinoma, which is diagnosed at an average age of 36 years. Therefore, being able to morphologically identify FH-d leiomyomas can triage a patient for genetic testing and appropriate management if needed.

References:

1. Reyes et al. Uterine smooth muscle tumors with features suggesting fumarate hydratase aberration. Mod Pathol. 2014; 27: 1020-1027.

2. Rabban et al. Prospective Detection of Germline Mutation of Fumarate Hydratase in Women With Uterine Smooth Muscle Tumors Using Pathology-based Screening to Trigger Genetic

Counseling for Hereditary Leiomyomatosis Renal Cell Carcinoma Syndrome A 5-Year Single Institutional Experience. Am J Surg Pathol. 2019; 43: 639-655.

3. Chan E et al. Detailed Morphologic and Immunohistochemical Characterization of Myomectomy and Hysterectomy Specimens From Women With Hereditary Leiomyomatosis and Renal Cell Carcinoma Syndrome (HLRCC). Am J Surg Pathol. 2019; 43: 1170-1179.

4. WHO Classification of Tumors of Female Reproductive Tract, 5th edition, 2020.5. Popp B et al. Targeted sequencing of FH-deficient uterine leiomyomas reveals biallelic

inactivating somatic fumarase variants and allows characterization of missense variants. Mod Pathol. 2020;33:2341-2353.

Case #3: Drs. Jasmine Vickery and Anna Biernacka

Diagnosis: Malignant Phyllodes with Heterologous Liposarcomatous Differentiation

Clinical History: The patient is a 36-year-old female with a medical history of fibromyalgia, polycystic ovarian syndrome, and tobacco use. Her past surgical history is notable for bilateral reduction mammoplasty in 2012 and excision of a fibroepithelial lesion in 2016. She now presents with a self-palpated and painful right breast mass.

Gross and microscopic findings: Grossly, the tumor was 9.5 cm in the greatest dimension. It was a solitary and well-defined mass that was tan-white, somewhat lobulated, and predominately firm and rubbery. There were translucent-gelatinous components that corresponded to myxoid areas microscopically. On the histologic examination, the tumor was heterogeneous and showed well-differentiated, myxoid, and pleomorphic components. There were foci of lipoblasts. A leaf-like architecture was focally apparent. The tumor cells showed clumped to dispersed chromatin, prominent nucleoli, and pale, eosinophilic to clear, and vacuolated cytoplasm. The mitotic rate in the pleomorphic areas was greater than 20 mitoses per 10 high power fields. Necrosis was identified, and overall, it comprised less than 10% of the tumor.

Differential Diagnosis: Malignant phyllodes Liposarcoma

o Myxoid o Well-differentiated o Dedifferentiated o Pleomorphic

Sarcomatoid carcinoma

Ancillary Studies: • IHC: Tumor cells were weakly positive for AE1/AE3 and P63. They were negative for MDM2, CDK4, CK5/6, MNF116, high-molecular-weight cytokeratins, CD34, HMB45, desmin, myogenin, CD45, S100, Estrogen receptor, and Bcl2.

• Molecular: The tumor was negative for MDM2 amplification by FISH. By next-generation sequencing, a loss of function mutation in the tumor suppressor BRCA2 was identified in the form of a rearrangement in exon 11. FBXW7, a ubiquitin ligase, was found to have a substitution mutation at the exon 5/ intron 4 boundary.

Discussion: Heterologous sarcomatous elements may be seen in the stroma of phyllodes tumors in up to 20% of cases. Adipocytic differentiation is the most common, and in the original case series by Rosen et al., foci of adipocytic differentiation occurred in approximately 7% of phyllodes tumors. All cases to date have been described in females, with a mean age of 48 years, and were unilateral. Grossly, tumors (mean size 11 cm) are usually well-circumscribed but may be infiltrative microscopically. They appear deep yellow in adipocytic components and lucent/gelatinous or fleshy in pleomorphic or myxoid components. In some cases, a clefted, leaf-like appearance may be evident on gross inspection. Microscopically, there are broad leaf-like formations, stromal hypercellularity, and atypia characteristic of phyllodes tumors. The malignant adipocytic component has a wide range of morphology identical to that seen in soft tissue sarcomas, including well-differentiated, myxoid, dedifferentiated, round cell and/or pleomorphic. A concurrent epithelial malignant component is rarely identified. By immunohistochemistry, cytokeratin markers are typically negative, but they may be focal and weak. This may be a significant pitfall in small biopsies. CD34 and S100 are variable and may be focally positive. Desmin, ER, Bcl2, and smooth muscle actin are negative. In all studies to date, MDM2 and CDK4 immunohistochemical stains have been negative in these neoplasms. The molecular biology is still unknown as MDM2 and CDK4 overexpression typically seen in atypical lipomatous tumor/well-differentiated liposarcoma and dedifferentiated liposarcoma are negative. No recurrent chromosomal aberrations or FUS-DDIT3 translocations characteristic of myxoid liposarcoma have been described. Wide surgical excision is the mainstay of therapy. The overall recurrence rate in one study was 14%. The features associated with the development of recurrence included histologic classification as a pleomorphic liposarcoma and microscopic infiltrative growth margins. Grade progression (tumor becoming higher grade) during local recurrence of phyllodes tumors can occur. Similar to its soft tissue counterparts, histologic features are important for prognosis, and patients with well-differentiated liposarcomatous elements have a better prognosis than those with pleomorphic components. Metastases are hematogenous (lung, bone, heart, liver, etc.) and occur in less than 10% of the cases within 2 years of the initial surgery. Lymph node metastases can occur but are exceptionally rare.

References:

1. Polat, Y, et al. Case Report: presentation of pleomorphic liposarcoma arising in a borderline phyllodes tumor. International journal of surgery case reports 53 (2018): 490-494.

2. Rosen PP., et al. Fibroepithelial neoplasms, in: P.P. Rosen (Ed.), Rosen’s Breast Pathology, 2nd ed., JB Lippincott, Philadelphia, 2001, pp. 176–200. 

3. Lyle PL, et al . Liposarcomatous differentiation in malignant phyllodes tumours is unassociated with MDM2 or CDK4 amplification. Histopathology. 2016;68(7):1040-1045.  

4. Austin RM, et al. Liposarcoma of the breast: a clinicopathologic study of 20 cases. Hum Pathol. 1986;17:906–913.

5. Powell CM, et al. Adipose differentiation in cystosarcoma phyllodes: a study of 14 cases. Am J Surg Pathol. 1994;18:720–72

6. Bacchi CE, et al. Lipophyllodes of the breast. A reappraisal of fat-rich tumors of the breast based on 22 cases integrated by immunohistochemical study, molecular pathology insights, and clinical follow-up. Ann Diagn Pathol. 2016 Apr;21:1-6.

7. Briski LM, at al. Primary Breast Atypical Lipomatous Tumor/ Well-Differentiated Liposarcoma and Dedifferentiated Liposarcoma. Arch Pathol Lab Med. 2018 Feb;142(2):268-274.

8. Tan BY, at al. Phyllodes tumours of the breast: a consensus review. Histopathology. 2016 Jan;68(1):5-21.

9. Liu Z, at al. A Comprehensive Immunologic Portrait of Triple-Negative Breast Cancer. Transl Oncol. 2018 Apr;11(2):311-329.

10. Kovac, M, et al. Exome sequencing of osteosarcoma reveals mutation signatures reminiscent of BRCA deficiency. Nat Commun 6, 8940 (2015).

Case #4: Drs. Tanner Storozuk and John Hart

Diagnosis: Colon polyps in Cowden syndrome

Clinical History: The patient is a 60-year-old female with a past medical history of HSIL and breast cancer in 2015. Her past surgical history is notable for a left partial mastectomy for invasive ductal carcinoma, SBR grade III. She now presents for her second screening colonoscopy. 10 colonic polyps were identified.

Gross and Microscopic Findings: Intraoperatively, the following polyps were noted: one 5 mm, sessile polyp in the ascending colon, eight small, semi-pedunculated polyps were found in the descending and transverse colon and one 5 mm, sessile polyp in the sigmoid colon. Microscopically, tubular adenomas and hamartomatous polyps were seen. The hamartomatous polyps showed both lipomatous and fibrous rich components. The fibrous rich hamartomatous polyps showed a prominent spindle cell proliferation within the lamina propria. The intramucosal lipomas showed adipocytic proliferation within the mucosa and above the muscularis propria.

Differential Diagnosis:

Colonic hamartomatous polyp with lipomatous component

Air insufflation – Pseudolipomatosis Intraoperatively done to help remove difficult polyps

Intramucosal lipoma

Underlying submucosal lipoma extending up into mucosa

Colonic hamartomatous polyp with fibrous rich component

Non-descript, spindle cell rich stroma. Histologically indistinct from prolapse-type polyps.

Ancillary Studies: S100 can be used to confirm adipose tissue and identifying neuromatous stroma. EMA, SMA, and CD34 can be used to identify stromal cell lineage in gastrointestinal hamartomatous polyps (i.e. fibroblastic/myofibroblastic).

Discussion: Cowden syndrome represents a relatively rare (prevalence of about 1:200-250:000) genetic disorder with a constellation both benign and malignant tumors across numerous different organs. It is classically defined by a mutation in the PTEN gene of chromosome 10 from which its alter ego PTEN hamartomatous tumor syndrome is derived. It is inherited in an autosomal dominant fashion and therefore affects males and females equally. Although a PTEN mutation is only identified in 25-35% Cowden syndrome patients, the constellation of findings within a given patient is often used to suggest further genetic workup.

The diagnostic criteria for Cowden Syndrome are separated into major and minor categories. A combination of major and minor criterion yields an operational diagnosis of Cowden syndrome is used to suggest further genetic testing. Various pre-test probability calculators exist to predict the likelihood that a patient will have a PTEN mutation. Most notably, gastrointestinal hamartomas fall into the major criterion alongside more common solid organ malignancies like breast, thyroid and endometrial cancer. A pathologist’s awareness of the various types of gastrointestinal manifestations of Cowden syndrome are often essential in suggesting further genetic workup.

Typical gastrointestinal manifestations seen in Cowden syndrome are esophageal glycogenic acanthosis and ganglioneuromas. More recently, intramucosal lipomas have been described in a series of Cowden syndrome patients. Although not diagnostically challenging, these may be overlooked due to the utilization of air insufflation during colonoscopy to remove polyps. S100 immunohistochemistry can be used to confirm the adipocytes are sitting within the mucosa and not procedural artifact. Caliskan et al. looked at a case series of twenty-five intramucosal lipomas. Interestingly, five of these cases (20%) were of patients with the diagnosis of Cowden syndrome. PTEN mutations were identified in four of the five cases. Intramucosal lipomas in the right clinical context can suggest further workup for Cowden syndrome.

A larger review of all gastrointestinal pathologies seen in Cowden syndrome patients highlighted additional findings. The cases series looked at 43 patients with Cowden syndrome and the spectrum of gastrointestinal manifestations. Cowden syndrome patients most commonly had hamartomatous polyps (85%) followed by serrated polyps (62%), conventional adenomas (48%) and inflammatory type polyps (21%). The hamartomatous polyps seen in the lower GI tract most commonly have ganglio-neuromatous (52%) or lipomatous (52%) components. Less commonly they had fibrous rich (14%) components. Immunohistochemistry with S-100 and CD34 is useful in subtyping the hamartomatous polyps. Histologically, the fibrous-rich hamartomatous polyps are non-descript and cannot be distinguished from more common prolapse type polyps. The clinical context is essential.

In summary, intramucosal lipomas represent a commonly missed, yet diagnostically significant entity in Cowden syndrome. Additionally, other hamartomatous polyps when combined with past medical history may be used to suggest the diagnosis of Cowden syndrome. Establishing a diagnosis of Cowden syndrome can lead to genetic testing and is necessary to enroll the patient, their siblings and offspring in age appropriate cancer surveillance.

References:

1. Wong NACS, O'Mahony O. Intramucosal fat is uncommon in large bowel polyps but raises three differential diagnoses. Journal of Clinical Pathology 2019;72:562-565.

2. Caliskan A, Kohlmann WK, Affolter KE, Downs-Kelly E, Kanth P, Bronner MP. Intramucosal lipomas of the colon implicate Cowden syndrome. Mod Pathol. 2018;31(4):643-651. doi:10.1038/modpathol.2017.161

3. Gammon A, Jasperson K, Kohlmann W, Burt RW. Hamartomatous polyposis syndromes. Best Pract Res Clin Gastroenterol. 2009;23(2):219-231. doi:10.1016/j.bpg.2009.02.007

4. Pilarski R, Stephens JA, Noss R, et al. Predicting PTEN mutations: an evaluation of Cowden syndrome and Bannayan–Riley–Ruvalcaba syndrome clinical features. Journal of Medical Genetics 2011;48:505-512.

5. Borowsky J, Setia N, Rosty C, et al. Spectrum of gastrointestinal tract pathology in a multicenter cohort of 43 Cowden syndrome patients. Modern Pathology: an Official Journal of the United States and Canadian Academy of Pathology, Inc. 2019 Dec;32(12):1814-1822. DOI: 10.1038/s41379-019-0316-7.

Case #5: Drs. Meghana Agni, Nicole Cipriani, and Peter Pytel

Diagnosis: Angiomatoid fibrous histiocytoma

Clinical History: A 51-year-old man presented to an outside hospital with a painful lump on his upper back that grew rapidly over the course of a few weeks and became visible through his clothing. His pain worsened without relief from any medication. He presented to the University of Chicago with a 30 lb weight loss over 3 months, fatigue, severe iron-deficiency anemia (Hgb 6.2 g/dL), and newly-diagnosed type 2 diabetes mellitus. MRI showed a 5.6 x 4.3 x 3.6 cm left paraspinal soft tissue mass at the T9-L1 levels, with a lobulated growth pattern and a mixed solid and cystic appearance. There was evidence of hemorrhage and erosive changes near the T10 spinous process. He had an initial biopsy followed by surgical resection. At the time of resection, it was noted that the mass wrapped around the spinous processes extending to the lamina of T12 and L1, firmly adherent to the lamina and the paraspinous muscles.  There appeared to be cortical destruction and invasion into the spinous processes of T11, T12, and L1. Representative sections of the mass are submitted for review.

Differential Diagnosis:

Organizing hemangioma Follicular dendritic cell sarcoma Lymph node metastasis, carcinoma or melanoma Ewing sarcoma Rhabdomyosarcoma Malignant extrarenal rhabdoid tumor Angiomatoid fibrous histiocytoma Myoepithelial tumor of soft tissue

Microscopic Findings:

Well-circumscribed, lobular architecture, with lobules separated by thinner fibrous septae and surrounded by dense fibrous stroma

Peripheral lymphoplasmacytic infiltrates (cuffs) Blood-filled spaces lined by, sometimes flattened, tumor cells Histiocytoid cells with ovoid nuclei, inconspicuous nucleoli, pale eosinophilic cytoplasm, ill-

defined cell borders Minimal mitoses and cytologic atypia

Immunohistochemical Findings:

AE1/AE3, CAM5.2, S100, SOX10, GFAP negative Desmin, EMA, CD68 patchy positivity CD99, diffuse membranous expression Calponin, equivocal cytoplasmic staining INI-1, BRG-1 retained

Molecular Findings:

EWSR1-ATF1 fusion by next generation sequencing

Discussion: We present a growing paraspinal soft tissue mass in a 51-year-old male associated with unrelenting pain and systemic symptoms including weight-loss, fever, and anemia. MRI revealed a lobular, mixed solid and cystic soft tissue mass at the T9-L1 levels with hemorrhagic and erosive changes and focal destructive infiltration into the spinous processes. Microscopically, a well-circumscribed, cystic and solid lesion with lobulated architecture was seen. The lobules were separated by fibrous septae and surrounded by dense, fibrous stroma along with peripheral lymphoplasmacytic infiltrates. Variably-sized blood-filled spaces were visible at low power. At high power, these spaces were not lined by endothelium. The tumor cells were medium-sized with ovoid nuclei, inconspicuous nucleoli and varying amounts of eosinophilic cytoplasm, creating a syncytial appearance.

The differential diagnosis was broad. Prominent blood-filled spaces gave the appearance of a vascular lesion at low power. Organizing hemangioma entered the differential but was dismissed upon recognition that the spaces were not lined by endothelium. The presence of peripheral lymphoplasmacytic aggregates hinted at potential lymph node metastasis. The cellular morphology opened the differential to mesenchymal tumors including follicular dendritic cell sarcoma, Ewing sarcoma, rhabdomyosarcoma, malignant extrarenal rhabdoid tumor, angiomatoid fibrous, histiocytoma, and myoepithelial tumor of soft tissue.

Desmin positivity ruled out follicular dendritic cell sarcoma (which is desmin negative), retention of INI-1 ruled out malignant extra-renal rhabdoid tumor (which shows INI-1 loss), and negativity for cytokeratins, SOX-10, and S100 precluded carcinoma or melanoma lymph node metastases. Ewing sarcoma, rhabdomyosarcoma, angiomatoid fibrous histiocytoma, and myoepithelial tumor of soft tissue were left in our differential. At this point, molecular analysis by next generation sequencing revealed EWSR1-ATF1 fusion. Notably, knowledge of the fusion gene partner (ATF1) provided important information. There are 17 documented tumors with EWSR1 rearrangements, but only 6 with ATF1 as a partner; angiomatoid fibrous histiocytoma and myoepithelial tumor of soft tissue are among these six. Our specimen matched the characteristic morphologic, molecular, and clinical features of angiomatoid fibrous histiocytoma. Furthermore, only one case of EWSR1-ATF1 fusion has been reported in myoepithelial tumor of soft tissue.

Angiomatoid fibrous histiocytoma was first described by Enzinger et al. in 1979 as angiomatoid malignant fibrous histiocytoma, but the word ‘malignant’ was dropped because of an approximately 1% rate of locoregional metastasis. In general, this tumor has good prognosis when treated with surgical excision, and the WHO calls it a neoplasm of intermediate (rarely metastasizing) biologic potential. It constitutes a well-circumscribed soft tissue lesion in the deep dermis or subcutis of the extremities, typically in children and young adults, but can appear in adults in the head, neck, trunk, and rarely visceral soft tissue sites. Like in our patient, it can be associated with pain and systemic symptoms, particularly weight-loss, fever, chills, fatigue, and severe anemia. Characteristic microscopic findings include a well-circumscribed, lobular architecture, pseudocapsule, lymphoplasmacytic cuff, pseudoangiomatoid spaces, and ovoid, bland tumor cells, with varying amounts of eosinophilic cytoplasm, indistinct cell borders, low mitotic index, and minimal cytologic atypia. Immunohistochemical staining is generally non-specific, but the combination of desmin and EMA expression raises suspicion for this entity. Finally, EWSR1 fusions are present in 76% of cases, usually with CREB1 or ATF1 as partners, and FUS-ATF1 fusions in the remaining cases.

References

1. Costa MJ, Weiss SW. Angiomatoid malignant fibrous histiocytoma. A follow-up study of 108 cases with evaluation of possible histologic predictors of outcome. Am J Surg Pathol. Dec 1990;14(12):1126-32.

2. Enzinger FM. Angiomatoid malignant fibrous histiocytoma: a distinct fibrohistiocytic tumor of children and young adults simulating a vascular neoplasm. Cancer. Dec 1979;44(6):2147-57. doi:10.1002/1097-0142(197912)44:6<2147::aid-cncr2820440627>3.0.co;2-8

3. Fanburg-Smith JC, Miettinen M. Angiomatoid "malignant" fibrous histiocytoma: a clinicopathologic study of 158 cases and further exploration of the myoid phenotype. Hum Pathol. Nov 1999;30(11):1336-43. doi:10.1016/s0046-8177(99)90065-5

4. Fletcher CD. Angiomatoid fibrous histiocytoma. Am J Surg Pathol. Apr 1992;16(4):426-7. doi:10.1097/00000478-199204000-00012

5. Flucke U, Mentzel T, Verdijk MA, et al. EWSR1-ATF1 chimeric transcript in a myoepithelial tumor of soft tissue: a case report. Hum Pathol. May 2012;43(5):764-8. doi:10.1016/j.humpath.2011.08.004

6. Tanas MR, Rubin BP, Montgomery EA, et al. Utility of FISH in the diagnosis of angiomatoid fibrous histiocytoma: a series of 18 cases. Mod Pathol. Jan 2010;23(1):93-7. doi:10.1038/modpathol.2009.138

7. Thway K, Fisher C. Angiomatoid fibrous histiocytoma: the current status of pathology and genetics. Arch Pathol Lab Med. May 2015;139(5):674-82. doi:10.5858/arpa.2014-0234-RA

8. Thway K, Fisher C. Mesenchymal Tumors with EWSR1 Gene Rearrangements. Surg Pathol Clin. Mar 2019;12(1):165-190. doi:10.1016/j.path.2018.10.007

9. Van Zwam P, Mentzel T, Flucke U. ALK Expression in Angiomatoid Fibrous Histiocytoma: Confirmation of the Findings of Cheah et al. Am J Surg Pathol. 08 2019;43(8):1156. doi:10.1097/PAS.0000000000001263

10. Wang Z, Zhang L, Ren L, et al. Distinct clinicopathological features of pulmonary primary angiomatoid fibrous histiocytoma: A report of four new cases and review of the literature. Thorac Cancer. Dec 2020;doi:10.1111/1759-7714.13727

11. Xiang Y, Carreon CK, Guerrero J, Putra J. TLE-1 immunoreactivity in angiomatoid fibrous histiocytoma: a potential diagnostic pitfall. Pathology. Oct 2020;52(6):722-725. doi:10.1016/j.pathol.2020.06.017

12. Ying LX, Teng XD. Myxoid and reticular angiomatoid fibrous histiocytoma: a case confirmed by fluorescence in situ hybridization analysis for EWSR1 rearrangement. Int J Clin Exp Pathol. 2018;11(6):3186-3190.

Case #6: Drs. Heather Smith and Peter Pytel

Diagnosis: Anaplastic astrocytoma with piloid features

Clinical History: The patient is a 34-year-old male with no significant past medical history who presented with two months of progressive headache, nausea, vertigo, ataxia, dysarthria, and dysgraphia. His neurological exam was remarkable for mild right sided weakness and dysmetria. His initial head CT showed an isodense lesion in the right cerebellar hemisphere with associated mass effect concerning for neoplasm. MRI brain with and without contrast confirmed the presence of an infiltrative, heterogeneously enhancing right cerebellar lesion with associated vasogenic edema and mass effect, including effacement of the fourth ventricle and herniation of the right cerebellar tonsil. The patient underwent both stereotactic biopsy and subsequent suboccipital craniotomy for resection of the lesion.

Differential Diagnosis:

High grade astrocytoma, IDH wild type High grade astrocytoma, IDH mutant Pleomorphic xanthoastrocytoma Pilocytic astrocytoma Pilocytic astrocytoma with anaplasia

Microscopic Findings and Ancillary Studies:

Microscopic Findings:

Infiltrative growth pattern

T1 +C

RR

T2 FLAIR

PXA-like nuclear atypia consisting of large cells with enlarged, hyperchromatic, eccentric nuclei or multiple nuclei

Increased proliferative activity No necrosis or microvascular proliferation

Immunohistochemistry findings:

GFAP positivity confirms astrocytic lineage IDH1 R32H negative p53 wildtype pattern Ki-67 to confirm increased proliferative activity

Molecular features:

NF1 c.3758_3762del ATRX c.4700-1G>A CDKN2A/B deletion Negative for IDH1/2, BRAF, p53, EGFR, or TERT promoter mutations Characteristic signature based on whole genome methylation profiling.

Discussion: We present an infiltrative posterior fossa tumor in a 34-year-old male with nuclear pleomorphism, an immunoprofile consistent with astrocytic lineage, CKDN2A loss, and ATRX and NF1 alterations. Together, these findings are consistent with high grade astrocytoma with piloid features, a recently characterized entity that is not in the 2016 World Health Organization (WHO) classification of central nervous system tumors but will be included in the upcoming iteration.

Historically, anaplastic astrocytoma was defined morphologically as an infiltrative astrocytic tumor with increased mitotic activity but without the necrosis or microvascular proliferation that defines glioblastoma. Central nervous system tumors are now increasingly being defined by their molecular features, which tend to have more impact on their biological behavior and prognosis than their morphological features. Based on the 2016 WHO classification and c-IMPACT-NOW guidelines infiltrating astrocytic tumors are often thought of as falling into two main categories – IDH wildtype and IDH mutant. Most of the adult IDH wildtype tumors exhibit similar molecular findings as those exhibited in IDH wildtype glioblastomas and also show similar behavior. There are, however, tumors like this one that do not fit well into any of the categories outlined by the WHO system. Some of these are being recognized as specific rare tumors based on special testing like whole genome methylation profiling. High grade astrocytoma with piloid features, also known as anaplastic astrocytoma with piloid features, is such a recently characterized type of IDH wildtype glioma. It has a predilection for the posterior fossa of young to middle-aged adults – 74% of them occur in the cerebellar hemispheres, with the remainder occurring supratentorially (17%) or in the spine (7%). They have not yet been assigned a grade in the WHO classification system. From a prognostic standpoint, however, they tend to be better than conventional IDH wildtype glioblastoma but worse than pilocytic astrocytoma, pleomorphic xanthoastrocytoma (PXA), or IDH-mutant anaplastic astrocytoma.

Morphologically, these lesions are somewhat variable. Approximately 40% will be at least focally GBM-like or focally piloid, while the remaining 10% will be at least focally PXA-like. About a third can have eosinophilic granular bodies (EGBs) or Rosenthal fibers. Consistent features include moderate to high

cellularity, an infiltrative growth pattern, and increased mitotic activity (which can be subtle, as low as 1-2 mitotic figures per 10 HPF). Helpful immunohistochemical stains include GFAP or Olig2 to confirm glial lineage, IDH1 R132H to help rule out IDH-mutant glioma, BRAFV600E to help rule out PXA, and Ki-67 to confirm increased proliferative activity in small biopsies with indistinct mitotic figures. Molecular testing most frequently shows CDKN2A/B deletions, ATRX mutations, MAPK pathway alterations such as mutations in NF1, KRAS, and FGFR1, and sometimes KIAA1549:BRAF fusions as well as gains of chromosomes 12q and 17q or losses of 1p, 8p, and 19q. EGFR, p53, and TERT promoter mutations common in conventional IDH-wildtype glioblastoma are not frequently seen. Roughly half of them show MGMT promoter methylation as well. Whole genome methylation profiling shows a completely distinct signature from other lesions that show morphologic overlap, such as PXA, pilocytic astrocytoma, and GBM. These tumors are therefore now thought to be a distinct entity rather than anaplastic transformation of pilocytic astrocytoma.

In summary, anaplastic astrocytoma with piloid features has morphology that varies from piloid to GBM-like to PXA-like (as in our presented case). Additionally, presence of CDKN2A/B deletions, ATRX mutations, or MAPK pathway alterations (i.e. NF1 mutations) helps to confirm the diagnosis.

References

1. Reinhardt A, Stichel D, Schrimpf D, et al. Anaplastic astrocytoma with piloid features, a novel molecular class of IDH wildtype glioma with recurrent MAPK pathway, CDKN2A/B and ATRX alterations. Acta Neuropathol. 2018 Aug;136(2):273-291. doi: 10.1007/s00401-018-1837-8. Epub 2018 Mar 21. PMID: 29564591.

2. Reinhardt A, Stichel D, Schrimpf D, et al. Tumors diagnosed as cerebellar glioblastoma comprise distinct molecular entities. Acta Neuropathol Commun. 2019 Oct 28;7(1):163. doi: 10.1186/s40478-019-0801-8. PMID: 31661039; PMCID: PMC6816155.

3. Louis DN, Wesseling P, Aldape K, et al. cIMPACT-NOW update 6: new entity and diagnostic principle recommendations of the cIMPACT-Utrecht meeting on future CNS tumor classification and grading. Brain Pathol. 2020 Jul;30(4):844-856. doi: 10.1111/bpa.12832. Epub 2020 Apr 19. PMID: 32307792.

4. Brat DJ, Aldape K, Colman H, et al. cIMPACT-NOW update 3: recommended diagnostic criteria for "Diffuse astrocytic glioma, IDH-wildtype, with molecular features of glioblastoma, WHO grade IV". Acta Neuropathol. 2018 Nov;136(5):805-810. doi: 10.1007/s00401-018-1913-0. Epub 2018 Sep 26. PMID: 30259105; PMCID: PMC6204285.