Pure epithelioid PEComas (so-called epithelioid angiomyolipoma) of the kidney: A clinicopathologic study of 41 cases: detailed assessment of morphology and risk stratification.

Epithelioid angiomyolipomas (perivascular epithelioid cell tumors) of the kidney are defined as potentially malignant mesenchymal lesions that are closely related to classic angiomyolipoma. Although approximately 120 cases are published, mostly as case reports with variably used diagnostic criteria, the pathologic prognostic predictors of outcome are unknown. We analyzed the clinicopathologic parameters in a large series of 41 cases of pure epithelioid angiomyolipomas of the kidney, which we designate as pure (monotypic) epithelioid PEComas to contrast them from classic angiomyolipomas that are regarded by some as PEComas. We use the terminology "pure" to separate these cases from those that may have variable epithelioid components. The mean age of the patients was 40.7 years (range, 14 to 68 y). The male-to-female ratio was 1:1. Seventy-nine percent of patients were symptomatic at presentation with metastatic disease at onset in 12 cases. Follow-up and/or disease progression information were available for 33 of 41 cases (mean, 44.5 mo and median, 24.5 mo; range, 4 to 240); 9 patients had a history of associated tuberous sclerosis. Recurrence and metastasis were seen in 17% and 49% of patients; 33% of patients died of disease. Lymph node involvement was seen in 24% of patients; the liver (63%), lung (25%), and mesentery (18.8%) were the most common metastatic sites. Clinicopathologic parameters associated with disease progression (recurrence, metastasis, or death due to disease) in univariate analysis included associated tuberous sclerosis complex or concurrent angiomyolipoma (any metastasis, P=0.046), necrosis (metastasis at diagnosis, P=0.012), tumor size >7 cm (progression, P=0.021), extrarenal extension and/or renal vein involvement (progression, P=0.023), and carcinoma-like growth pattern (progression, P=0.040) (the 5 adverse prognostic parameters for pure epithelioid PEComas). Tumors with <2 adverse prognostic parameters (13 cases) were considered to be low risk for progression tumor, with 15% having disease progression. Tumors with 2 to 3 adverse prognostic parameters (14 cases) were considered to be "intermediate risk," with 64% having disease progression. Tumors with more than 4 or more adverse prognostic parameters (6 cases) were considered to be high risk, with all patients having disease progression. Of tumors with 3 or more adverse prognostic parameters, 80% had disease progression. An exact logistic regression analytic model showed that only carcinoma-like growth pattern and extrarenal extension and/or renal vein involvement were significant predictors of outcome (P=0.009 and 0.033, respectively). Our data of a large series with uniform definitional criteria confirm the malignant potential for pure epithelioid PEComas and provide adverse prognostic parameters for risk stratification in these patients.