Bladder carcinoma with shadow cell differentiation: a case report with immunohistochemical analyses.

A peculiar case of bladder carcinoma showing shadow cell differentiation (SCD) in a 72-year-old man is presented. The tumor histologically revealed high grade urothelial carcinoma (UC) and partially contained squamous component with a transition to shadow cell nests, similar to those seen in cutaneous pilomatricoma (PMX). Immunohistochemically, the modes of cell death in the component of SCD were identical to those in PMX. The present case as well as 10 cases of cutaneous PMX showed nuclear expression of beta-catenin, whereas 10 cases of bladder UC with squamous differentiation revealed membranous localization without nuclear expression. These results suggest that nuclear accumulation of beta-catenin may play an important role for SCD in the present case. SCD in extracutaneous tumor is extremely rare and, in the literature, the present case is the second one as for bladder carcinoma.