Low PCA3 expression is a marker of poor differentiation in localized prostate tumors: Exploratory analysis from 12,076 patients

// Mohammed Alshalalfa 1 , Gerald W. Verhaegh 2, 3 , Ewan A. Gibb 1 , Maria Santiago-Jimenez 1 , Nicholas Erho 1 , Jennifer Jordan 1 , Kasra Yousefi 1 , Lucia L.C. Lam 1 , Tyler Kolisnik 1 , Jijumon Chelissery 1 , Roland Seiler 1, 4 , Ashley E. Ross 5 , R. Jeffrey Karnes 6 , Edward M. Schaeffer 7 , Tamara T. Lotan 8 , Robert B. Den 9 , Stephen J. Freedland 10 , Elai Davicioni 1 , Eric A. Klein 11 and Jack A. Schalken 2, 3 1 GenomeDx Biosciences Inc., Vancouver, BC, Canada 2 Department of Urology, Radboud University Medical Center, Nijmegen, The Netherlands 3 Radboud Institute for Molecular Life Sciences, Nijmegen, The Netherlands 4 Department of Urologic Sciences, University of British Columbia, Vancouver, BC, Canada 5 James Buchanan Brady Urological Institute, Johns Hopkins Hospital, Baltimore, MD, USA 6 Department of Urology, Mayo Clinic, Rochester, MN, USA 7 Department of Urology, Feinberg School of Medicine, Northwestern University, Chicago, IL, USA 8 Department of Pathology and Oncology, Johns Hopkins School of Medicine, Baltimore, MD, USA 9 Sidney Kimmel Cancer Centre, Thomas Jefferson University, Philadelphia, PA, USA 10 Department of Surgery, Division of Urology, Center of Integrated Research on Cancer and Lifestyle, Samuel Oschin Comprehensive Cancer Center, Cedars Sinai Medical Center, Los Angeles, CA, USA 11 Glickman Urological & Kidney Institute, Cleveland Clinic, Cleveland, OH, USA Correspondence to: Mohammed Alshalalfa, email: mohamed@genomedx.com Keywords: prostate cancer, PCA3, initial biopsy, prognosis, under-diagnosis Received: November 16, 2016      Accepted: January 10, 2017      Published: February 07, 2017 ABSTRACT Background: Prostate cancer antigen 3 ( PCA3 ) is a prostate cancer diagnostic biomarker that has been clinically validated. The limitations of the diagnostic role of PCA3 in initial biopsy and the prognostic role are not well established. Here, we elucidate the limitations of tissue PCA3 to predict high grade tumors in initial biopsy. Results: PCA3 has a bimodal distribution in both biopsy and radical prostatectomy (RP) tissues, where low PCA3 expression was significantly associated with high grade disease (p<0.001). PCA3 had a poor performance of predicting high grade disease in initial biopsy (GS≥8) with 55% sensitivity and high false negative rates; 42% of high Gleason (≥8) samples had low PCA3 . In RP, low PCA3 is associated with adverse pathological features, clinical recurrence outcome and greater probability of metastatic progression (p<0.001). Materials and Methods: A total of 1,694 expression profiles from biopsy and 10,382 from RP patients with high risk tumors were obtained from the Decipher Genomic Resource Information Database (GRIDTM)prostate cancer database. The primary clinical endpoint was distant metastasis-free survival for RP and high Gleason grade for biopsy. Logistic regression analyses and Cox proportional hazards models were used to evaluate the association of PCA3 with clinical variables and risk of metastasis. Conclusions: There is high prevalence of high grade tumors with low PCA3 expression in the biopsy setting. Therefore, urologists should be warned that using PCA3 as stand-alone test may lead to high rate of under-diagnosis of high grade disease in initial biopsy setting.