Prostatic apudomas are represented by well-, moderately- and poorly differentiated variants. Histologic differentiation determines various functional properties of tumor cells. Tumor cells of well-differentiated apudomas produce serotonin, less frequently calcitonin, poorly differentiated ones produce only ACTH. Apud cells of moderately differentiated tumors, besides their main function to synthesize biogenic amines and hormones (serotonin, ACTH) possess immunoreactivity to epithelial membrane antigen, carcinoembryonal antigen and prostatic specific antigen.