Evaluation of B7-H3 Expression as a Biomarker of Biochemical Recurrence After Salvage Radiation Therapy for Recurrent Prostate Cancer

Abstract

The ability to predict which men will experience biochemical recurrence (BCR) after salvage radiation therapy (SRT) for recurrent prostate cancer (PCa) remains less than optimal. Related to this, novel targets for adjuvant therapies are also lacking. Here, we evaluate the association of B7-H3 expression in primary PCa tumors and BCR after SRT. We identified 148 patients who received SRT between July 1987 and July 2003. Expression of B7-H3 in primary PCa tumors was detected using a monoclonal antibody. The staining levels were quantified via visual assessment and categorized as weak, moderate, or marked. Relative risks (RRs) and 95% confidence intervals (CIs) from Cox proportional hazards models were used to examine the association between B7-H3 staining and BCR. With a median follow-up of 6.2 years (minimum, 0.6; maximum, 14.7), 78 patients (53%) experienced BCR. In single-variable analysis, there was evidence of an increased risk of BCR for patients with moderate (RR, 2.25; 95% CI, 1.24-4.09, p = 0.008) and marked (RR, 4.40, 95% CI, 2.29-8.43, p < 0.001) B7-H3 staining compared with weak staining. This evidence remained, albeit weaker, after adjustment for additional clinicopathologic covariates (RR, 1.82, p = 0.068 [moderate vs. weak]; RR, 2.87, p = 0.003 [marked vs. weak]). This is the first report that higher tumor B7-H3 staining in primary PCa tumors is associated with increased risk of BCR after SRT. Future studies involving larger numbers of patients are required to validate these results and also to explore possible means of targeting B7-H3 in an adjuvant setting.