Oncocytic Papillary Renal Cell Carcinoma in the Background of Renal Adenomatosis.

Renal adenomatosis is a rare disease characterized by numerous adenomas in bilateral kidneys. A literature review shows that malignant tumors can arise in this condition. The present case describes an oncocytic papillary renal cell carcinoma (PRCC) arising in renal adenomatosis. A 70-year-old man presented with incidentally identified, multiple right renal masses on computed tomography. Right nephrectomy was performed, and the resected kidney revealed numerous radiologically undetected small nodules additionally. Microscopically, the nodules were papillary neoplasms of variable sizes and cytological features. The largest nodule measured 1.6 cm and was composed of oncocytic cells, meeting the diagnostic criteria of oncocytic PRCC. The smaller nodules of papillary adenomas and tiny lesions showing a single papillary ingrowth were also seen. This case exhibits a spectrum of renal papillary neoplasms in a resected kidney and can be a valuable case in the understanding of tumorigenesis.