Primary adenocarcinoma of the renal pelvis: histologic features of a stepwise process from intestinal hyperplasia to dysplasia in a patient with chronic renal abscess.

Pure adenocarcinomas of the urothelium are very rare and their location in the pelvis is uncommon. Although their pathogenesis is not well defined, adenocarcinomas are likely to originate from neoplastic transformation of the glandular cells of the urothelial intestinal metaplasia usually arising in response to chronic irritating stimuli, such as long-duration inflammation, urolithiasis, and hydronephrosis. We report a case of an 81-year-old woman who underwent right nephrectomy for relapsing renal abscess due to a staghorn calculus. Histological examination disclosed an infiltrating adenocarcinoma arising from a tubulovillous adenoma with the surrounding pelvic mucosa showing a sequence of intestinal metaplasia, low- and high-grade villous adenoma, and invasive adenocarcinoma, supporting the hypothesis of cancer progression due to chronic inflammation from the urothelium through the metaplasia step.