Immunodiagnosis by prostatic acid phosphatase to differentiate primary male breast cancer from metastatic prostate cancer.

A patient who was treated with estrogens for carcinoma of the prostate was later diagnosed with apparent primary cancer of the male breast. He received chest-wall radiation therapy with curative intent. Later, immunodiagnosis by immunoperoxidase staining for human prostate-specific acid phosphatase of the breast tissue revealed that the patient actually had metastatic prostate cancer to the breast rather than primary breast cancer secondary to estrogen therapy. Use of highly specific peroxidase-antiperoxidase tissue staining for human prostate-specific acid phosphatase is recommended to differentiate primary male breast cancer from metastatic prostate cancer.