[777] Intratumoral Fat and Concomitant Angiomyolipoma: A Potential Pitfall in Staging and Diagnosis of Renal Cell Carcinoma

M Aron, H Aydin, L Sercia, C Magi-Galluzzi, M Zhou. Cleveland Clinic, Cleveland, OH

Background: The pathologic stage is one of the most important prognostic factors for renal cell carcinoma (RCC). If a tumor extends into perirenal fat or sinus, it is staged as pT3a. Intratumoral fat and angiomyolipomas (AML) occurring within renal cell neoplasms have been reported in literature, mainly in the context of radiologic differential diagnosis of AML. However, these lesions may be mistaken for invasion into perinephric or sinus fat or mis-diagnosed as sarcomatoid RCC if the concomitant AML is smooth muscle predominant. We report a series of 15 such cases to highlight the potential pitfall in staging and diagnosis associated with intratumoral fat and concomitant AML.
Design: Nephrectomies between January1992 to September 2009 were reviewed for the following morphological features: intratumoral fat/AML, location of the fat/AML, number of foci, size of the largest focus, interphase with the tumor, presence of osseous metaplasia and chronic inflammation.
Results: 13 renal cell neoplasms had intratumoral fat, including clear cell RCC (10), chromophobe RCC (1), papillary RCC (1), and oncocytoma (1). 7 cases (53.9%) had a single focus of fat while the remaining 6 (46.15%) showed 2 or more foci. The size of the largest focus of fat ranged from 0.1 to 1.8 mm. Six (46.2%) cases had fat within the center of the tumor while the remaining 7 (53.9%) cases had fat located peripherally, either near the capsule (3 cases), renal sinus (1 case) or both (3 cases). Chronic inflammation and osseous metaplasia were identified in 7 (53.9%) and 8 (61.5%) cases, respectively. 2 clear cell RCC cases had intratumoral AML foci, both of which were located at the periphery of the tumor. In one case, AML had a significant spindle cell component.
Conclusions: Intratumoral fat and AML can be found in renal cell neoplasms. When present, they are often found at the periphery of RCC and can potentially be mistaken for invasion into perinephric or sinus fat. The presence of chronic inflammation may further raise the suspicion for desmoplastic response as the result of invasion by RCC. Smooth muscle predominant AML found within RCC may be mistaken for sarcomatoid differentiation. Pathologists should be aware of such staging and diagnostic pitfalls. Osseous metaplasia is seen in about 60% of intratumoral fat and helps recognize the lesion as metaplastic.
Category: Genitourinary (including renal tumors)

Wednesday, March 24, 2010 9:30 AM

Poster Session V # 87, Wednesday Morning


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