PSMA expression is highly homogenous in primary prostate cancer

BACKGROUND: Prostate-specific membrane antigen (PSMA) is a suggested target for antibody-based therapy of prostate cancer, potentially involved in the regulation of cell migration. As heterogeneity may limit the applicability of targeted therapies, this study was undertaken to estimate the degree of heterogeneity of PSMA expression in prostate cancer.

METHODS: For heterogeneity analysis, a prostate cancer heterogeneity TMA containing samples from 10 different tumor blocks of 189 consecutive prostate cancers was used. PSMA expression was analyzed by immunohistochemistry.

RESULTS: PSMA expression was found in 97.6% of 1171 interpretable tissue spots including 260 (22.2%) with weak, 345 (29.5%) with moderate, and 538 (45.9%) with strong positivity. On a patient level, a positive PSMA immunostaining was found in 172 of 173 analyzable patients (99.4%) with at least a weak staining reaction. PSMA immunostaining was homogenously positive in 161 prostate cancers (93.6%), whereas heterogenous PSMA positivity was seen in 11 of 172 positive cases (6.4%). In these cases, heterogeneity was intrafocal in 8 cases (72.7%) and interfocal in 27.3% cases. PSMA expression was completely absent in 1 patient.

CONCLUSIONS: Given the high frequency and high homogeneity of PSMA expression in prostate cancer, we conclude that increased PSMA expression may occur early in prostate cancer development. High homogeneity of PSMA expression is a strong argument for a high utility of PSMA as a prostate cancer drug target.