Lipid-laden foamy macrophages in renal cell carcinoma. Potential frozen section diagnostic pitfall

Abstract

Lipid-laden foamy macrophages are characteristic of xanthogranulomatous pyelonephritis (XGP). We have encountered a case of renal cell carcinoma (RCC), with extensive necrosis, in which confluent sheets of foamy macrophages were a dominant feature. We describe the case and discuss the potential frozen section diagnostic problem in attempting to distinguish between confluent sheets of xanthoma cells a "reactive" change in RCC and xanthoma cells as a fundamental component of XGP. We propose that awareness of that problem should prompt the pathologist to request additional samples.