Objectives. To assess the utility of alpha-methylacyl-coenzyme A racemase (AMACR), also known as P504S, immunohistochemistry in the detection of postradiation prostatic adenocarcinoma in surgical specimens. Pathologic diagnosis of postradiation prostate cancer is difficult because of the radiation-induced cytologic changes in benign and malignant epithelial cells. AMACR/P504S is a recently identified molecular marker for prostatic adenocarcinoma. It has been demonstrated that AMACR is overexpressed in the vast majority of prostatic adenocarcinoma cases by cDNA microarray, RNA analysis, Western blotting, and immunohistochemistry. Methods. A total of 80 prostate glands, including 40 irradiated prostate specimens (28 with adenocarcinoma and 12 benign prostates) and 40 nonirradiated prostate specimens (20 with adenocarcinoma and 20 benign prostates), were examined. The specimens were obtained after salvage radical prostatectomy (n = 25), transurethral resection (n = 4), or needle biopsy (n = 11). All samples were immunohistochemically analyzed for AMACR. Results. All 48 carcinoma cases (28 of 28 irradiated and 20 of 20 nonirradiated specimens) showed strongly positive AMACR/P504S immunostaining. AMACR immunostaining was negative for all irradiated (n = 12) and nonirradiated (n = 20) benign prostates, as well as the irradiated benign glands adjacent to carcinoma. 34βE12 confirmed the presence of basal cells in all benign prostates (32 of 32) and the absence of basal cells in carcinoma (0 of 48). Conclusions. Our results demonstrate that AMACR is a highly specific and sensitive indicator of postradiation prostate cancer. AMACR immunostaining facilitates the challenging differentiation between prostatic adenocarcinoma and radiation-induced atypia in benign prostatic epithelium and may be of exceptional value in limited needle biopsies.
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