Optimizing Target Volume for Adjuvant Radiation Therapy in Penile Cancer

Abstract

Recent studies have reported improved outcomes with adjuvant radiation therapy in penile cancer. However, the appropriate target volumes to be irradiated in this group of patients for optimal outcomes are still unclear. This study aims to report the patterns of failure and define target volumes to be irradiated in patients with pN3 penile cancer. Patients with pT1-T4, pN3, cM0, and squamous cell carcinoma of the penis who received adjuvant radiation therapy (involved field or extended field), with or without concurrent chemotherapy were included in the study. Complete information on disease characteristics, radiation therapy target details, and patterns of failure were available for 75 patients. Disease-free (DFS) and overall survival (OS) were estimated using the Kaplan-Meier method, and log-rank test was used to compare survival outcomes between the involved field and extended field radiation therapy groups. Multivariate analysis was performed using the Cox proportional hazards model to analyze factors correlating with survival outcomes. At a median follow-up of 39 months, 38.6% (29/75) of patients had relapsed either locally, regionally, or at distant sites. Of the 24 patients who received extended field radiation therapy (EFRT), only 1 (4%) patient experienced relapse. Twenty-eight (55%) patients experienced relapse after involved-field radiation therapy (IFRT), of which 28.5% were regional-only relapses and 64% relapses were associated with a regional component. The 2-year DFS and OS of the entire cohort were 62.2% and 70.8%, respectively. The 2-year DFS was 67.9% in patients who received IFRT and 94.1% in those who received EFRT (P=.002), and the 2-year OS was 62.4% with IFRT and 91.1% with EFRT (P=.014). Extended field radiation therapy was associated with an improved DFS (hazard ratio, 12.2; 95% confidence interval, 1.5-97.4; P=.02) and OS (hazard ratio, 4.6; 95% confidence interval, 1-21.5; P=.05) on multivariate analysis. Extended field radiation therapy significantly improves clinical outcomes compared with involved-field radiation in patients with pN3 penile cancer.