Renal Cell Carcinomas With Intratumoral Fat and Concomitant Angiomyolipoma

Abstract

Intratumoral fat and angiomyolipomas (AMLs) occurring within renal cell carcinomas (RCCs) have rarely been reported but may be mistaken for tumor invasion into perinephric or renal sinus fat or misdiagnosed as tumor exhibiting sarcomatoid differentiation. We report 16 such cases. In 14 RCC cases, there was intratumoral fat, 9 of which had fat located peripherally near the capsule (n = 6), renal sinus (n = 1), or both (n = 2). Inflammatory infiltrates and osseous metaplasia were identified in the intratumoral fat in 7 and 8 cases, respectively. Two cases had intratumoral AML foci located at the periphery of RCC. Intratumoral fat or AML at the periphery of RCC simulated the invasion into the fat, while the smooth muscle component of AML resembled spindle cell, or sarcomatoid, differentiation. Our study highlights the potential pitfalls in staging and diagnosis when intratumoral fat or AML is found within RCC.

Sclerosing TFEB -rearrangement renal cell carcinoma: a recurring histologic pattern

“…[10,12] However, rare calcification in angiomyolipoma has been reported. [10] Despite that positivity for melanocytic markers and cathepsin K would be a shared feature of both TFEB translocation renal cell carcinoma and angiomyolipoma, the tumor cells in this case were negative for smooth muscle…”

Histogram Analysis of Small Solid Renal Masses: Differentiating Minimal Fat Angiomyolipoma From Renal Cell Carcinoma

“…Cholesterol necrosis, osseous metaplasia, and incorporation of perinephric fat have also been described in rare malignant masses that can simulate angiomyolipoma because of the presence of macroscopic fat. In these rare cases, calcification is often present and indicates malignancy [12,[14][15][16][17][18][19][20][21][22]. There also is the unusual possibility of an aggressive epithelioid form of angiomyolipoma that has a malignant course.…”

Composite renal cell carcinoma and angiomyolipoma in a patient with Tuberous sclerosis: A diagnostic dilemma

“…Only 15 cases have been reported, in which both the components were within the same tumour mass. 2,6,7 Two of these had a sharply circumscribed lesion of RCC within an AML, 2,3 2 were RCCs with AML at the periphery, with admixture of tumor components, 6 and the remaining did not mention whether the RCC and AML components were intermingled. [7][8][9] In our case, both these components were closely intermingled (composite tumour), which adds to its rarity.…”

“…As rightly pointed out by Aron and colleagues, the lipomatous areas of the AML component may be mistaken for perinephric fat or renal sinus fat invasion in a classical RCC, resulting in upstaging of the tumour. 6 A spindle cell predominant AML, particularly one showing degenerative nuclear atypia, may be mistaken for sarcomatoid RCC, which again has worse outcomes. Further, epithelioid component of AML may be misinterpreted as RCC.…”