Renal cell carcinoma arising in a long pre-existing angiomyolipoma

Angiomyolipoma (AML) is a mixed mesenchymal tumor belonging to the family of perivascular epithelioid cell tumors. Concurrent development of AML and adult renal cell carcinoma (RCC) is very rare. Herein is presented a unique case in which RCC arose within a previously detected AML tumor mass. A 40-year-old woman had been diagnosed with AML of the right kidney. Fifteen years later, during a regular radiographic examination, a new lesion was detected at the lower pole of the right kidney adjacent to the previously described AML. Because RCC was clinically suspected, the patient underwent right nephrectomy. Macroscopically, the tumor had a yellowish, transparent, fatty area and an opaque yellowish area with cystic features. Microscopically, the former tumor, consisting of an admixture of mature adipose tissue with smooth muscle and vascular tissue, was diagnosed as AML. The latter tumor was diagnosed as RCC (clear cell type). RCC was not completely enclosed within the AML, but overlapped it. No fibrous capsule was found between these tumors. Although this situation is very rare, from a clinical and pathological point of view it is important to consider the possibility that RCC might arise within AML. The relationship between the two lesions is discussed with a review of the literature.