Application of Alpha-methylacyl Coenzyme a Racemase Immunohistochemistry: a Help or Hindrance in the Diagnosis of Prostate Cancer?

Since the discovery of alpha-methylacyl CoA racemase (AMACR) in prostate cancer in 2000, there have been a number of publications studying the diagnostic value of this enzyme. Although the role of this enzyme is still unknown, the application of AMACR immunohistochemistry in pathology practice has been increased sharply in the last few years. We are going to review the recent studies of the AMACR expression in prostate cancer and several benign and malignant entities by us and other investigators. Then we will discuss clinical application, limitation and pitfall of using this marker in details. This discussion is by no means a guidance for pathology practice, but it may provide some reference when interpretating AMACR immunostaining. INTRODUCTION Widespread use of PSA has resulted not only in increased number of prostate needle core biopsies performed each year, but also an increasing number of small foci of uncertain diagnoses of limited biopsy material (1-3). Although histological features of prostatic adenocarcinoma such as growth pattern, nuclear atypia, absence of basal cells, and presence of characteristic extra cellular material are important (4-5), when used alone, they are not entirely sensitive or specific to establish a definitive diagnosis of prostate cancer. Immunohistochemical stains for high-molecular weight keratins such as 34beta12 and more recently p63 have been used to identify basal cells which are typically present in benign glands but absent in prostatic adenocarcinoma (6-). Unfortunately, negative staining for basal cells in a few suspicious glands is not a definitive proof of malignancy, as benign conditions can have a patchy or discontinuous distribution of basal cells (8). Rarely, prostatic adenocarcinoma may also contain cells positive for basal cell markers. Therefore, a sensitive yet specific “positive” marker of prostatic adenocarcinoma would be very useful in raising the confidence level in diagnosis on limited specimens for prostate needle cores.