A 35-year-old woman with a right kidney mass underwent CT-guided needle core biopsy. Histologic sections show a neoplasm comprised of pleomorphic epithelioid cells with eosinophilic cytoplasm, with occasional bizarre nuclei and variably prominent nucleoli. Mitotic figures are easily appreciated. The neoplastic cells lack expression of PAX8, CK7, CK20, P63, and GATA3. Follow-up immunohistochemical stains show the neoplastic cells are positive for cathepsin-K and Melan-A, and a diagnosis of epithelioid angiomyolipoma (EAML) was made.
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The morphology and immunophenotypic profile of this neoplasm are consistent with an epithelioid angiomyolipoma (EAML). These account for approximately 5% of angiomyolipoma. The current WHO diagnostic criteria requires at least 80% of the neoplastic cells to have an epithelioid morphology to classify as EAML. These tumors express cathepsin-K and melanocytic markers (HMB45 and Melan-A). Variable expression of smooth muscle markers is also reported.
The majority of EAML are associated with genetic alterations in mTOR pathway (TSC2 gene more than TSC1 gene) that can arise secondary to somatic or germline alterations. Rare instances can show TFE3 gene rearrangements. Recent studies show metastatic EAML are enriched with alterations of TP53, RB, and ATRX genes.1 Immunohistochemistry can serve as surrogate markers for these genetic alterations and can be of use as prognostic indicators. Mutant patterns include loss of expression of RB, loss of expression of ATRX, and loss or diffuse expression of p53. This case showed loss of RB expression, retained ATRX, and equivocal p53 expression. These results strongly suggest loss of RB gene and raise concern for an EAML with an aggressive clinical behavior. Close follow-up was recommended.
Sarwat Gilani, M.B.B.S.
Fellow, Genitourinary Pathology
Sounak Gupta, M.B.B.S., Ph.D.
Consultant, Anatomic Pathology
Associate Professor of Laboratory Medicine and Pathology
Assistant Professor of Pathology
Mayo Clinic College of Medicine and Science