AMACR

AMACR (P504S protein, 48 kDa) plays a role in the beta-oxidation of branched-chain fatty acids and their derivatives. AMACR is found in mitochondria and peroxisomes of numerous tissues such as prostate, liver, biliary tract, kidney and lung. Using immunohistochemistry, non-neoplastic prostate show a weak or focal staining reaction in about 20% of the cases. The reactivity tends to decrease with age but the correlation coefficient is low.

A diffuse staining pattern for AMACR has been found in more than 90% of prostate carcinomas irrespective of Gleason score. Particularly foamy, pseudohyperplastic and atrophic variants of carcinoma may be negative. In prostatic intraepithelial neoplasia (PIN), the positive rate of AMACR ranges from 13% to 72%.

AMACR is mainly used in prostate lesions. Since negative staining for high molecular weight cytokeratin (HMW-CK) in atypical prostate glands may not be sufficient for a definitive diagnosis of malignancy, p63 may enhance the ability to diagnose limited prostate cancer. However, AMACR should always be used in conjunction with (HMW-CK) and/or p63. A cocktail staining is applicable. It is also important to note that AMACR positive glands in a prostate biopsy may represent seminal vesicle or periurethral glands.

Kidney is recommended as positive tissue control for AMACR: Virtually all epithelial cells of the proximal tubules must show a strong and distinct granular cytoplasmic staining, whereas epithelial cells of the distal tubules must display a weak granular cytoplasmic staining reaction. Normal prostate is recommended as negative tissue control for AMACR: The epithelial cells must be negative or only show a focal staining reaction.

Gologan A, Bastacky S, McHale T, Yu J, Cai C, Monzon-Bordonaba F, Dhir R. Age-Associated Changes in Alpha-Methyl CoA Racemase (AMACR) Expression in Nonneoplastic Prostatic Tissues. Am J Surg Pathol. 2005 Nov;29(11):1435-41.

Hameed O, Humphrey PA. p63/AMACR antibody cocktail restaining of prostate needle biopsy tissues after transfer to charged slides: a viable approach in the diagnosis of small atypical foci that are lost on block sectioning. Am J Clin Pathol. 2005 Nov;124(5):708-15.

Jiang Z, Woda BA. Diagnostic utility of alpha-methylacyl CoA racemase (P504S) on prostate needle biopsy. Adv Anat Pathol. 2004 Nov;11(6):316-21.

Kunju LP, Chinnaiyan AM, Shah RB. Comparison of monoclonal antibody (P504S) and polyclonal antibody to alpha methylacyl-CoA racemase (AMACR) in the work-up of prostate cancer. Histopathology. 2005 Dec;47(6):587-96.

Varma M, Jasani B. Diagnostic utility of immunohistochemistry in morphologically difficult prostate cancer: review of current literature. Histopathology. 2005 Jul;47(1):1-16.