Prostate cancer (PC) is a common malignancy and a leading cause of cancer-associated mortality among males in Western countries. Novel diagnostic and prognostic biomarkers for PC are urgently needed to prevent overdiagnosis and overtreatment of nonaggressive tumors. In this study, we investigated the biomarker potential of ANPEP in PC. ANPEP encodes a membrane-bound zinc-dependent protease termed aminopeptidase N (APN), which belongs to a group of widely expressed ectopeptidases. Expression of APN protein was determined by immunohistochemical analysis of tissue microarrays, including PC specimens from 267 radical prostatectomy (RP) patients and 199 conservatively treated (CT) patients as well as several nonmalignant prostate and metastatic PC samples. Clinical endpoints were recurrence-free survival (RFS) and cancer-specific survival (CSS), respectively. ANPEP promoter methylation was analyzed in parallel by quantitative methylation-specific PCR (qMSP/MethyLight) in approximately 250 nonmalignant and PC tissue samples. We found that APN protein expression was significantly lower in localized PC and further reduced in metastatic PC, compared to nonmalignant prostate tissue samples. Aberrant ANPEP promoter hypermethylation was observed in approximately half of all PC samples investigated. Methylation levels correlated inversely with APN immunoreactivity, suggesting that ANPEP is epigenetically silenced in PC. By multivariate analysis, negative APN immunoreactivity was significantly associated with short RFS in the RP cohort (HR=0.24; p=0.002) and with short CSS in the CT cohort (HR=0.23; p=0.049), in both cases independently of routine predictors such as Gleason score, T stage and PSA. Combining APN with a known angiogenesis marker (vascular endothelial growth factor (VEGF) immunoreactivity or microvessel density (MVD)) in a simple two-marker model improved risk prediction significantly in both cohorts. ANPEP promoter methylation did not show significant prognostic value in the RP cohort (p=0.09) and was not investigated in the CT cohort. In conclusion, our results indicate that a simple immunohistochemical test for APN may add significant prognostic value to currently used routine predictors for PC outcome. Furthermore, our findings suggest that it may be favorable to use APN in combination with an established angiogenesis marker to improve risk stratification and separate patients with clinically localized PC into low, intermediate and high risk subgroups in order to guide treatment decisions. Finally, we have identified ANPEP as a new common target for promoter hypermethylation in PC, indicating that epigenetic mechanisms contribute to downregulation of ANPEP in PC cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3636. doi:1538-7445.AM2012-3636