Comparison of a low-cost immunohistochemistry marker panel with a cell-cycle progression assay for the prediction of outcome after radical prostatectomy.

Abstract

118 Background: Gene expression assays appear to stratify prostate cancer risk, however tests involving amplification techniques are expensive and may strain payment systems. We aimed to compare the prognostic utility of a low-cost immunohistochemistry (IHC) panel consisting of three validated markers with an RNA expression based cell-cycle progression (CCP) score. Methods: Among 5,748 patients with PCa within an institutional database, we identified 424 with localized PCa treated with radical prostatectomy (RP). IHC analysis was performed using tissue microarrays to examine the expression status of PTEN, Ki67, and ERG compared with previously calculated CCP scores derived from 31 genes normalized to 15 housekeeper genes. Associations of IHC status, CCP scores, adjusted for clinical and pathologic characteristics (Cancer of the Prostate Risk Assessment Score, CAPRA-S) were performed using Cox proportional hazards regression to examine risk of biochemical recurrence (BCR), and metastasis or PCa- specific mortality (PCSM). We compared models using concordance index (c-index) testing. Results: Median age at treatment was 59 years and patients were followed for a median of 114 months post RP. By 10 years after RP, 27% experienced BCR and 4% developed metastasis or PCSM. Adjusted for CAPRA-S, the triad of PTEN loss, high Ki67, and positive ERG expression was independently associated with risk of BCR (HR 2.3, 95% CI 1.1-4.7) and metastasis/PCSM (HR 8.3, 95% CI 3.3-21.2). In a model including CAPRA-S, IHC panel, and CCP, the CCP score was independently associated with both recurrence and metastasis/PCSM (HR 1.9, 95% CI 1.5-2.5 and HR 2.5, 95% CI 1.5-4.1, respectively), but IHC expression status of PTEN/Ki67/ERG remained an independent predictor of both endpoints. The addition of the CCP assay marginally improved the c-index of a combined IHC and CAPRA-S model from 0.78 to 0.81 for the prediction of metastasis/PCSM. Conclusions: A low-cost three-marker IHC panel examining PTEN, Ki67, and ERG expression was independently associated with downstream PCa endpoints following RP. Efforts are warranted to reduce the cost of PCa prognostic tools in order to expand access.