Extramedullary haemopoiesis usually occurs in association with haematological disorders—in particular, myelofibrosis—and normally occurs in the reticulo-endothelial system, involving the liver, spleen, and lymph nodes. The kidneys and other organs are less often affected. In addition, single lineage haemopoiesis may occur, although it does not usually form mass-like lesions. This report describes a focus of erythropoiesis occurring in a renal cell carcinoma.

A 55 year old woman underwent a right radical nephrectomy and the specimen measured 10 × 6 × 6 cm. A …