Purpose: External-beam radiation therapy (EBRT) may predispose to secondary malignancies that include bladder cancer (BCa), rectal cancer (RCa), and lung cancer (LCa). We tested this hypothesis in a large French Canadian population-based cohort of prostate cancer patients.
Methods and materials: Overall, 8,455 radical prostatectomy (RP) and 9,390 EBRT patients treated between 1983 and 2003 were assessed with Kaplan-Meier and Cox regression analyses. Three endpoints were examined: (1) diagnosis of secondary BCa, (2) LCa, or (3) RCa. Covariates included age, Charlson comorbidity index, and year of treatment.
Results: In multivariable analyses that relied on incident cases diagnosed 60 months or later after RP or EBRT, the rates of BCa (hazard ratio [HR], 1.4; p = 0.02), LCa (HR, 2.0; p = 0.004), and RCa (HR 2.1; p <0.001) were significantly higher in the EBRT group. When incident cases diagnosed 120 months or later after RP or EBRT were considered, only the rates of RCa (hazard ratio 2.2; p = 0.003) were significantly higher in the EBRT group. In both analyses, the absolute differences in incident rates ranged from 0.7 to 5.2% and the number needed to harm (where harm equaled secondary malignancies) ranged from 111 to 19, if EBRT was used instead of RP.
Conclusions: EBRT may predispose to clinically meaningfully higher rates of secondary BCa, LCa and RCa. These rates should be included in informed consent consideration.
Crown Copyright 2010. Published by Elsevier Inc. All rights reserved.