We report the clinicopathologic, immunohistochemical, ultrastructural, and genetic features of an unusual renal
tumor composed of large, atypical, densely packed, clear/eosinophilic epithelioid cells. Three patients, two men and one woman (ages 31, 36, and 60 years of age, respectively), had
abdominal pain. Morphologically, all cases showed aggressive features (largeness, atypical cells, sarcomatoid features,
necrosis, and, in one case, invasion of the renal vein). Despite the marked morphologic resemblance of these
tumors to high-grade
sarcomatoid renal cell carcinoma, their phenotype (HMB45+, CD68+/-, actin+/-, and
vimentin and
keratin negative) is in contrast to that observed in epithelial
tumors and parallels the phenotypic profile of
angiomyolipoma. Ultrastructural analysis showed the presence of
glycogen, mitochondria, and prominent electron-dense, membrane-bound granules in the neoplastic cells, and the absence of melanosomes or premelanosomes. Genetic study, performed using polymerase chain reaction from
paraffin sections, showed a loss of heterozygosity at the TSC2-containing region on 16p in one case, and on 3p in two cases, showing that multiple genetic alterations are taking place in these
tumors. Follow-up has shown local recurrence in one case after 6 years, and the patient died 1 year later of cardiorespiratory failure. The other two patients are well after 26 and 10 months. All three patients were evaluated for signs of
tuberous sclerosis, and findings were negative. We suggest that these
tumors should be considered close relatives of the
angiomyolipoma variants, composed purely of perivascular epithelioid cells. More cases and longer follow-up durations are needed to fully evaluate its prognostic implication.