Copy number alterations of P53, RB1, and MDM2 as prognostic markers in intermediate-risk prostate cancer.

Abstract

117 Background: We interrogated copy number alternations (CNA) of p53, Rb1 and MDM2 as prognostic determinants of biochemical failure in localized intermediate-risk prostate cancer. Methods: Using Affymetrix Oncoscan array technology, we characterized copy number alterations (CNA) for 284 D’Amico-classified intermediate-risk prostate cancers. Of the 284 patients, 143 underwent image-guided radiotherapy (IGRT), while 141 underwent radical prostatectomy (RadP). Biochemical-relapse free survival (bRFS) was assessed as a clinical end-point, with biochemical failure defined using the Phoenix and AUA criteria for IGRT and RadP patients, respectively. Results: We observed allelic losses ofp53 and Rb1 in 23.9% (n = 68) and 31.0% (n = 88) and allelic gains of MDM2 in 3.17% (n = 9) in our cohort, respectively. 7.7% (n = 22), 1.1% (n = 3) and 0.4% (n = 1) of all cases exhibited concurrent losses of p53 and Rb1, p53 loss and MDM2 gain, and concurrent p53/Rb1 loss and MDM2 gain, respectively. Patients with allelic losses of p53, Rb1 and allelic gain of MDM2 loci exhibited increased percent genome aberration (PGA) (Mean 9.2 vs. 6.1 p < 0.001; 10.1 vs. 5.4 p < 0.001; 18.1 vs. 6.5 p < 0.001 respectively). Rb1 loss and MDM2 gain were not significant predictors of bRFS, independent of treatment modality. Allelic loss of p53 was predictive of poor bRFS in the RadP cohort (HR = 1.86, 95% CI 1.10-3.16, p = 0.022), but not for IGRT patients (HR = 1.16, 95% CI 0.63-2.12, p = 0.629). Additionally, patients in the RadP cohort with concurrent losses of p53 and Rb1 also had a higher likelihood of poorer bRFS (HR = 2.32, 95% CI 1.1-4.93, p = 0.029). On multivariate analysis, incorporating PGA and pre-treatment PSA, concurrent p53/Rb1 losses, but not single p53 loss, was prognostic for bRFS in patients who underwent RadP (p53/Rb1 losses, HR = 2.16, 95% CI 1.0-4.65, Wald's p = 0.05; p53loss, HR = 1.62, 95% CI 0.94-2.79, Wald's p = 0.08). Conclusions: In a cohort of men with intermediate-risk prostate cancers, we identified an unfavourable subgroup of patients harbouring concurrent copy number losses of p53 and Rb1 that was associated with an adverse prognosis of biochemical failure following radical prostatectomy.