Granular cell tumor expressing myogenic markers in the prostate

A granular cell tumor in the prostate of a 72 year old male is reported. The tumor nest was composed of large polygonal tumor cells, possessing cytoplasmic eosinophilic granules which were positive with PAS stain and resistant to diastase digestion. Immunohistochemically, most tumor cells were strongly positive with anti-alpha-smooth muscle actin and -neuron specific enolase antibodies. Only a few scattered tumor cells were reacted with anti-S-100 protein antibody. These findings might suggest smooth muscle differentiation of this case, and provide an additional insight into the histogenesis of granular cell tumors, especially in their heterogeneity.