Metanephric adenoma and solid variant of papillary renal cell carcinoma: common and distinctive features

Abstract

Aims To evaluate morphological and immunohistochemical (IHC) features helpful in distinguishing metanephric adenoma (MA) from solid papillary renal cell carcinoma (s‐PRCC). Methods and results We present a detailed study of 21 MA and 23 s‐PRCC. The two entities exhibited significant similarities, both being well‐circumscribed tumours composed of tightly packed small cells arranged in solid sheets or ill‐defined tubules, often presenting glomeruloid bodies, psammoma bodies and dystrophic calcification, and showing overlapping immunoreactivity for S100, CD57 and CK7. Conversely, most MA were non‐encapsulated, whereas most s‐PRCC showed a thick fibrous pseudocapsule; MA cells had scanty cytoplasm and a high nuclear:cytoplasmic ratio in comparison to s‐PRCC, where occasional tumour cells showed abundant cytoplasm and high nuclear grade. Polypoid branching fronds were common in MA, but absent in s‐PRCC; multifocality and papillary hyperplasia/adenoma were seen only in s‐PRCC. MA were positive for WT1 and negative for EMA and alpha‐methylacyl‐CoA racemase (AMACR); s‐PRCC were positive for EMA and AMACR and negative for WT1. Conclusions Despite overlapping features, careful morphological and architectural evaluation should result in accurate diagnosis of most MA and s‐PRCC. In challenging cases, IHC stains for WT1, EMA and AMACR may help in distinguishing these two entities.