This image shows clear cell adenocarcinoma arising in the urinary bladder. The tumor is composed of numerous tubulo-cystic structures lined by cuboidal or flat epithelial cells. Hobnail cells are also seen within some of the tubular structures. This tumor bears some resemblance to nephrogenic metaplasia (adenoma). Nuclear anaplasia, increased mitotic activity, and solid growth pattern favor clear cell adenocarcinoma over nephrogenic metaplasia. This distinction may be very challenging in small biopsy specimens.