Adenocarcinoma of the prostate simulating primary rectal malignancy

Adenocarcinoma of the prostate may occasionally mimic primary carcinoma of the rectum in both symptoms and gross character of the lesion. Establishment of the proper diagnosis is important because of the wide difference in treatment and prognosis. Since both tumors are adenocarcinomas, the biopsy specimen may be equivocal if the lesion is anaplastic, and the diagnosis may depend upon the history, metastatic picture, serum acid phosphatase, and response to estrogen therapy. Prostatic origin should be considered in rectal lesions, if the prostate gland is not palpably definable, separate from the mass.