Pathways Case Studies: August 2022

A man in his 70s presented with a slowly enlarging, painless testicular swelling and was found to have a 1.6 cm mass confined to the left testicle on imaging. Microscopic images and selected immunohistochemical stains are shown in Figures 1 and 2, respectively. Histologic sections showed a relatively well-circumscribed neoplasm, comprised of cords and tubules, without infiltrative growth. Interspersed spindled stromal elements and collagenous material (less than 50% of the lesion) were identified. The cytomorphology of the cord-like structures was significant for cells exhibiting clear, moderate to abundant cytoplasm and ovoid nuclei without atypia or increased mitotic activity. No germ cell neoplasia in situ (GCNIS) was identified in the background seminiferous tubules. The cells of interest showed nuclear localization of beta-catenin (Figures 2A and B) and steroidogenic factor 1 (SF1) (Figures 2C and D). In addition, these cells expressed pankeratin, vimentin, and inhibin (focal), and were negative for alpha fetoprotein, CD30, glypican 3, OCT 3/4, PLAP, SALL4, and WT1.

Figure 1: Multipanel
Figure 2: Multipanel

What would be the most likely diagnosis?

  • Seminoma
  • Sex cord-stromal tumor consistent with Sertoli cell tumor
  • Metastatic tumor
  • Adenomatoid tumor

The correct answer is ...

Sex cord-stromal tumor consistent with Sertoli cell tumor.

Sertoli cell tumor (SCT) is a sex cord-stromal tumor of the testis, accounting for less than 1% of all testicular tumors. It is the second most common pure sex cord-stromal tumor, representing approximately one-third of sex cord-stromal tumors. It occurs most frequently in middle-aged Caucasian males, with a median age of approximately 40 years. Clinically, SCTs are detected incidentally on imaging or present with a combination of unilateral testicular mass, swelling, discomfort, and/or pain. Hormonal manifestations such as gynecomastia are relatively infrequent. Most cases are benign; however, approximately 5%-10% of tumors are malignant. Rarely, SCTs can initially manifest with a distant metastasis.1,2

Per the 2022 Word Health Classification, SCT, not otherwise specified (NOS) and large cell calcifying SCT, represent two major categories of SCTs.On histopathologic examination, SCT, NOS is characterized by an admixture of tubular, sheet-like, cord-like, and trabecular architecture. The neoplastic cells have round to ovoid nuclei with occasional nucleoli. These cells have clear to pale eosinophilic cytoplasm that is moderate to abundant.3 Necrosis, increased mitotic activity, cytological atypia, lymphovascular invasion, and infiltrative growth are typically absent. The presence of any of these features, along with large tumor size, is suggestive of a malignant SCT.1

The sclerosing variant of the SCT, NOS deserves further mention. This variant is characterized by a dense fibrocollagenous background, occupying more than 50% of the lesion. The architectural and cytomorphologic features of the sclerosing variant are essentially similar to conventional SCT, NOS; however, the cords, tubules, and clusters of cells appear embedded within and partially entrapped by the hypocellular stroma. Originally, the sclerosing variant was conceptualized as a distinctive variant separate from SCT, NOS, but it is currently considered under the umbrella of SCT, NOS due to overlapping CTNNB1 gene mutation and nuclear immunoreactivity for beta-catenin.1,4,5 Most of the cases of SCT, NOS, sclerosing variant follow a benign course.1-3 The case presented herein bears morphologic resemblance to the sclerosing variant; however, it was not classified as a sclerosing variant of the SCT, NOS because the sclerotic stroma represented less than 50% of the entire tumor.

On immunohistochemical examination, the majority of cases are positive for SF1, while nuclear β-catenin immunoreactivity is present in approximately two-thirds of the cases. Inhibin is positive in about half of the tumors. The absence of germ cell neoplasia in situ and negative staining for OCT 3/4 are helpful in ruling out a GCNIS-derived lesion.


  1. WHO Classification of Tumours Editorial Board. Urinary and male genital tumours [Internet]. Lyon (France): International Agency for Research on Cancer; 2022. (WHO classification of tumours series, 5th ed.; vol. 8). Available from:
  2. Al-Obaidy KI, Idrees MT. Testicular tumors: A contemporary update on morphologic, immunohistochemical and molecular features. Adv Anat Pathol. 2021;28:258-75.
  3. Kao CS, Kum JB, Idrees MT, Ulbright TM. Sclerosing Sertoli cell tumor of the testis: a clinicopathologic study of 20 cases. Am J Surg Pathol. 2014;38:510-7.
  4. Perrone F, Bertolotti A, Montemurro G, Paolini B, Pierotti MA, Colecchia M. Frequent mutation and nuclear localization of β-catenin in sertoli cell tumors of the testis. Am J Surg Pathol. 2014;38:66-71.
  5. Zhang C, Ulbright TM. Nuclear localization of β-catenin in Sertoli cell tumors and other sex cord-stromal tumors of the testis: An immunohistochemical study of 87 cases. Am J Surg Pathol. 2015;39:1390-4.
Photo of Burak Tekin, M.D.

Burak Tekin, M.D.

Resident, Anatomic and Clinical Pathology
Mayo Clinic

Sounak Gupta, M.B.B.S., Ph.D.

Consultant, Anatomic Pathology
Mayo Clinic
Associate Professor of Laboratory Medicine and Pathology
Assistant Professor of Pathology
Mayo Clinic College of Medicine and Science

  • 23-month-old boy
  • Right kidney mass 
  • Nephrectomy (gross): kidney >1kg; 15 cm fleshy, tan, encapsulated mass 
  • See histology (Figures 1 and 2) and molecular changes in BCOR (Figure 3) 
Figure 1: Low-power magnification of the lesion
Figure 2: High-power magnification of the lesion
Figure 3: Molecular findings

What is the diagnosis?

  • Wilms tumor
  • Clear cell sarcoma of the kidney
  • Renal cell carcinoma, clear cell type
  • Malignant rhabdoid tumor of the kidney

The correct answer is ...

Clear cell sarcoma of the kidney.

Clear cell sarcoma of the kidney (CCSK) is an uncommon neoplasm of young children (<5 years old; M:F::2:1).1 It is an aggressive tumor, often metastatic at presentation (bones are a common site).1 Histology is variable with a myxoid pattern seen in approximately 50% of the cases, and with plump tumor cells that can exhibit indistinct borders.2 By immunohistochemistry, these tumors are frequently positive for BCOR and Cyclin D1.3 The molecular profile is characterized by in-frame internal tandem duplications (ITDs) in BCOR, Xp11.4 (exon 15), in approximately 90% of the cases.4 Rarer abnormalities make up the remaining 10%, such as t(10;17) (q22;p13) YWHAE-NUTM2B/E.1 

BCOR (Bcl6 transcriptional corepressor) is an epigenetic regulator through histone modifications, important for germinal center B-cell development, tissue differentiation and chromatin remodeling.4 CCSK is one of the members of the “BCOR Family of Tumors,” which also includes Ewing sarcoma-like sarcomas/small blue round cell tumors with BCOR rearrangements.5 CCSK treatment is based on surgery, radio- and chemotherapy (highly responsive to doxorubicin).2 With treatment, 5-year survival is ~80%; relapses can happen in 15% of cases.1,2 

BCOR germline loss-of-function variants are associated with X-linked dominant oculo-facio-cardio-dental (OFCD) syndrome (prenatal lethality in hemizygous males) and X-linked recessive Lenz’s microphthalmia (attenuated variant).6

Incorrect answers:

Wilm’s tumor: triphasic histology (blastema, epithelial, and stromal elements); multiple altered genes have been described including WT1REST, and TRIM28. Alterations in loci 11p13 and 11p15 are associated with WAGR syndrome and Beckwith-Wiedemann syndrome, respectively.

Malignant rhabdoid tumor of the kidney: rhabdoid tumor cells, INI1 (SMARCB1) loss.

Renal cell carcinoma, clear cell type: typically, not seen in pediatric patients. 3p deletion (including VHL) is often seen. 


  1. Ueno-Yokohata H, Okita H, Nakasato K, et al. Consistent in-frame internal tandem duplications of BCOR characterize clear cell sarcoma of the kidney. Nat Genet. 2015 Aug;47(8):861-3. doi:10.1038/ng.3338
  2. Argani P, Perlman EJ, Breslow NE, et al. Clear cell sarcoma of the kidney: a review of 351 cases from the National Wilms Tumor Study Group Pathology Center. Am J Surg Pathol. 2000 Jan;24(1):4-18. doi:10.1097/00000478-200001000-00002
  3. Wong MK, Ng CCY, Kuick CH, et al. Clear cell sarcomas of the kidney are characterized by BCOR gene abnormalities, including exon 15 internal tandem duplications and BCOR–CCNB3 gene fusion. Histopathology. 2018 Jan;72(2):320-329. doi:10.1111/his.13366
  4. Astolfi A, Fiore M, Melchionda F, Indio V, Bertuccio SN, Pession A. BCOR involvement in cancer. Epigenomics. 2019 May;11(7):835-855. doi:10.2217/epi-2018-0195
  5. Kao YC, Owosho AA, Sung YS, et al. BCOR-CCNB3 fusion positive sarcomas. A clinicopathologic and molecular analysis of 36 cases with comparison to morphologic spectrum and clinical behavior of other round cell sarcomas. Am J Surg Pathol. 2018 May;42(5):604-615. doi:10.1097/PAS.0000000000000965
  6. Ng D, Thakker N, Corcoran CM, et al. Oculofaciocardiodental and Lenz microphthalmia syndromes result from distinct classes of mutations in BCOR. Nat Genet. 2004 Apr;36(4):411-6. doi:10.1038/ng1321
Photo of Alessia Buglioni, M.D.

Alessia Buglioni, M.D.

Fellow, Molecular Genetic Pathology
Mayo Clinic

Kevin Halling, M.D., Ph.D.

Consultant, Laboratory Genetics and Genomics
Mayo Clinic
Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science

A 39-year-old male patient with abdominal pain underwent a CT scan and was found to have a hepatic lesion, which on resection had an appearance demonstrated on H/E (Figure 1) and reticulin stain (Figure 2). It was further interrogated with immunostains shown below. 

Figure 1: H/E
Figure 2: Reticulin stain
Figure 3: β-catenin
Figure 4: CRP
Figure 5: HAA
Figure 6: LFABP

Which one of the following is the correct choice?

  • β-catenin activated hepatic adenoma
  • Inflammatory hepatic adenoma
  • HNF1A inactivated hepatic adenoma
  • Hepatic adenoma, unclassified type

The correct answer is ...

Hepatic adenoma, unclassified type.

As seen on H/E (Figure 1), there is some expansion of hepatic plate and focal acini formation but with a lack of cytologic atypia, uniformly condensed nuclei, and low N/C ratio, lack of prominent nucleoli, and preserved reticulin stain (Figure 2), supporting the diagnosis of hepatic adenoma. Immunostains obtained to classify the hepatic adenoma further show a normal membranous expression of β-catenin (Figure 3), which rules out β-catenin activated hepatic adenoma, which will show an abnormal nuclear expression of β-catenin. Expression of C-reactive protein (CRP) (Figure 4) is similar to the background liver, and hepatic amyloid A (Figure 5) expression is absent, which rules out inflammatory type hepatic adenoma. Liver-type fatty acid-binding protein (LFABP) expression (Figure 6) is preserved, which rules out the HNF1A inactivated hepatic adenoma. Hence the correct answer is a hepatic adenoma, unclassified type. 


  1. Balitzer D, Kakar S. Diagnostic challenges and risk stratification of hepatocellular adenoma. Diagn Histopathol. 2022;28(2):89-102.
  2. Torbenson MS. Diagnostic approach to well-differentiated hepatocellular carcinoma. Diagn Histopathol. 2022;28(2):69-78.
  3. Dhingra S, Fiel MI. Update on the new classification of hepatic adenomas: clinical, molecular, and pathologic characteristics. Arch Pathol Lab Med. 2014 Aug;138(8):1090-7. doi:10.5858/arpa.2013-0183-RA. PMID: 25076298
Square photo of Ameya Patil

Ameya Patil, M.B.B.S.

Resident, Anatomic and Clinical Pathology
Mayo Clinic

Lizhi Zhang, M.D.

Consultant, Anatomic Pathology
Mayo Clinic
Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science

An 11-year-old boy presented with progressive headache, nausea, and unsteady gait. He had no significant past medical or family history. Magnetic resonance imaging (MRI) of the brain revealed a 3.2 cm x 4.7 cm x 5.7 cm, heterogeneously enhancing mass centered within the right aspect of the fourth ventricle with inferior extension through the obex and right foramen of Luschka. No definitive restricted diffusion was identified. A resection of the tumor was performed.

Figure 1: T1 post-contrast (A) MRI demonstrates a 3.2 x 4.7 x 5.7 cm, heterogeneously enhancing, lobulated mass in the right aspect of the fourth ventricle with extension through the obex and right foramen of Luschka, partial effacement of the fourth ventricle, and mass effect on the adjacent cerebellum, pons, medulla, and cervicomedullary junction with associated FLAIR hyperintensity (B). 
Figure 2: Histologically, the tumor shows prominent perivascular pseudorosettes (A, scale bar 200 µm) composed of cells with indistinct borders and uniform, round nuclei, radially surrounding blood vessels with an intervening anucleate zone (B, scale bar 50 µm). Areas with necrosis (C, asterisk, scale bar 200 µm) and scattered mitotic figures (D, arrows, scale bar 100 µm) are present, but microvascular proliferation is not identified.
Figure 3: By immunohistochemistry, the tumor cells are diffusely positive for GFAP (A), negative for OLIG2 (B), and show focal EMA paranuclear dot-like staining (C, arrows, inset). H3 K27me3 is negative in tumor nuclei with retained expression in endothelial cells (D). H3 K27M is negative (E). The Ki-67 labeling index is low (F, all captions scale bar 100 µm).
Figure 4: Chromosomal microarray analysis shows a relatively balanced genome with 1q gain (encircled).

Which of the following is true regarding this neoplasm?

  • Is associated with a poor outcome.
  • Consistently shows MYCN amplification.
  • Affects predominantly adolescents and young adults.
  • Harbors frequent ZFTA gene rearrangements.

The correct answer is ...

Is associated with a poor outcome.

Posterior fossa (PF) ependymomas are circumscribed glial neoplasms that arise in the fourth ventricle and affect predominantly children, with a slight male predominance. Histologically, they typically show prominent perivascular pseudorosettes with tumor cells radially arranged around blood vessels with an intervening anucleate zone. True ependymal rosettes are present only in a minority of cases. Tumor cells show indistinct borders and uniform round-to-ovoid nuclei with speckled chromatin. Nuclear pleomorphism, vascular hyalinization, calcification, and microcystic change can be seen. Although clear cell change can be present, this is more frequently seen in supratentorial ependymomas. PF ependymomas can be assigned CNS WHO grades 2 or 3. Although grading criteria in ependymomas are not clearly defined, brisk mitotic activity and microvascular proliferation are considered high-grade histological features that carry greater prognostic significance over nuclear pleomorphism and tumor necrosis. PF ependymomas are positive for S100 and GFAP immunohistochemistry, while OLIG2 expression is usually focal to absent. EMA immunoreactivity can be seen in a paranuclear dot-like fashion. Focal keratin expression can also be seen. 

According to the 2021 WHO Classification of CNS Tumors, PF ependymomas are currently divided into two groups based on their clinical, histopathological, and molecular features, and DNA methylation profiling: posterior fossa group A (PFA) and posterior fossa group B (PFB) ependymomas. The diagnosis of PF ependymoma should be used when molecular analysis either is not feasible (not otherwise specified, NOS) or cannot assign a molecular group (not elsewhere classified, NEC).

Posterior fossa group A (PFA) ependymomas arise more frequently from the roof or lateral aspect of the fourth ventricle. They predominantly affect infants and young children with a median age of 3 years, in contrast to PFB ependymomas, which more frequently occur in older children and adolescents. Microscopically, PFA ependymomas show the histopathological features and immunoprofile described for PF ependymomas. High-grade features may be present in up to two-thirds of cases, and CNS grades 2 or 3 are assigned based on these features. 

PFA ependymomas show global reduction of H3 p.K28me3 (K27me3), but only approximately 4% of these tumors harbor H3 p.K28M (K27M) mutations. Reduction of H3 K27me3 can be assessed by surrogate immunohistochemistry as loss of expression in tumor cell nuclei, and retained H3 K27me3 expression in endothelial cells can be used as an internal control. Since variability in the proportion of tumor cells showing H3 K27me3 nuclear expression loss can be seen, a cut-off value of 80% positivity has been proposed, with tumors above this cut-off more likely to fall into the PFB group. 

Essential diagnostic criteria for PFA ependymomas include the histological features and immunoprofile of ependymoma, along with either reduction/loss of H3 K27me3 in tumor cell nuclei or a DNA methylation profile aligned with this molecular group. By genome-wide copy number analysis, PFA ependymomas usually show a stable genome. However, given its prognostic significance across all PF ependymomas, assessment for gain of chromosome 1q is recommended. Nonetheless, PFA ependymomas appear to be associated with a worse prognosis regardless of the chromosome 1q status. PFA ependymomas carry a poor outcome when compared to PFB ependymomas, and extent of surgical resection appears to be significantly associated with prognosis. 


  1. Sriram V, Pietsch T, Aldape KD, et al. Posterior fossa group A (PFA) ependymoma. In: WHO Classification of Tumours Editorial Board. Central nervous system tumours [Internet]. Lyon (France): International Agency for Research on Cancer; 2021. (WHO classification of tumours series, 5th ed.; vol. 6). Available from:
  2. Pajtler KW, Wen J, Sill M, et al. Molecular heterogeneity and CXorf67 alterations in posterior fossa group A (PFA) ependymomas. Acta Neuropathol. 2018 Aug;136(2):211-226.
  3. Panwalkar P, Clark J, Ramaswamy V, et al. Immunohistochemical analysis of H3K27me3 demonstrates global reduction in group-A childhood posterior fossa ependymoma and is a powerful predictor of outcome. Acta Neuropathol. 2017 Nov;134(5):705-714. 
  4. Godfraind C, Kaczmarska JM, Kocak M, et al. Distinct disease-risk groups in pediatric supratentorial and posterior fossa ependymomas. Acta Neuropathol. 2012 Aug;124(2):247-57.5.
  5. Pajtler KW, Witt H, Sill M, et al. Molecular Classification of Ependymal Tumors across All CNS Compartments, Histopathological Grades, and Age Groups. Cancer Cell. 2015 May 11;27(5):728-43.
Photo of Maria Adelita (Adelita) Vizcaino Villalobos, M.D.

Maria Adelita Vizcaino Villalobos, M.D. 

Fellow, Anatomical Pathology and Neuropathology
Mayo Clinic 

Aivi Nguyen, M.D.

Senior Associate Consultant, Anatomic Pathology
Mayo Clinic
Assistant Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science

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