Malacoplakia of the prostate confused with clear cell carcinoma.

Primary malacoplakia of the prostate is a rare benign disease, which is frequently mistaken for carcinoma and granulomatous prostatis. The surgical and clinical course of a patient with obstructive hypertrophy of the prostate is reviewed after an initial incorrect diagnosis of clear cell carcinoma. Experience in defining the lesion during the transurethral resection is presented. The pathogenesis, morphological structure and unique microscopic appearance of malacoplakia, characterized by large mononuclear cells associated with small laminated concretions, are described and illustrated.