The prostate-specific G-protein coupled receptors PSGR and PSGR2 are prostate cancer biomarkers that are complementary to α-methylacyl-CoA racemase

BACKGROUND. Immunohistochemistry (IHC) to detect α-methylacyl-CoA racemase (AMACR) expression can be useful in the diagnosis of small foci of prostate cancer on needle biopsy specimens, although it still has limitations in terms of both sensitivity and specificity. We have previously described the increased expression of two prostate-specific G-protein coupled receptors (PSGR and PSGR2) in human prostate cancer. To examine their potential usefulness as cancer biomarkers, we have evaluated their expression relative to AMACR in prostate cancer tissues. METHODS. Expression of PSGR, PSGR2, and AMACR were examined by quantitative reverse-transcriptase PCR in mRNAs from benign prostate and prostate cancer tissues. Expression of PSGR2 and AMACR was also examined by in situ hybridization using a prostate cancer tissue microarray. RESULTS. By in situ hybridization, 24 of 40 prostate cancer cases showed concordant expression of PSGR2 and AMACR. However, in 16 cases there was significant discordance between expression levels of these two markers. By quantitative RT-PCR all three markers were substantially increased in cancer, with AMACR the most overexpressed (30-fold), followed by PSGR2 (13-fold) and PSGR (10-fold). AMACR was the best single marker of prostate cancer but in 7 of the 59 total cases the expression of AMACR was not significantly elevated while PSGR and/or PSGR2 were substantially elevated. CONCLUSION. All three biomarkers are increased in prostate cancer but their expression is not completely concordant. There is a subset of cases in which analysis of expression of PSGR and/or PSGR2, in addition to AMACR, would be diagnostically useful.