Prostate brachytherapy and second primary cancer risk: a competitive risk analysis

Purpose To assess the risk of second primary cancer (SPC) after [125I]iodine prostate cancer brachytherapy compared with prostatectomy and the general population. Patients and Methods In a cohort consisting of 1,888 patients with prostate cancer who received monotherapy with brachytherapy (n = 1,187; 63%) or prostatectomy (n = 701; 37%), SPC incidences were retrieved by linkage with the Dutch Cancer Registry. Standardized incidence rates (SIRs) and absolute excess risks (AERs) were calculated for comparison. Results A total of 223 patients were diagnosed with SPC, 136 (11%) after brachytherapy and 87 (12%) after prostatectomy, with a median follow-up of 7.5 years. The SIR for all malignancies, bladder cancer, and rectal cancer were 0.94 (95% CI, 0.78 to 1.12), 1.69 (95% CI, 0.98 to 2.70), and 0.90 (95% CI, 0.41 to 1.72) for brachytherapy and 1.04 (95% CI, 0.83 to 2.28), 1.82 (95% CI, 0.87 to 3.35), and 1.50 (95% CI, 0.68 to 2.85) for prostatectomy, respectively. Bladder SPC risk was significantly increased after brachytherapy for patients age 60 years or younger (SIR, 5.84; 95% CI, 2.14 to 12.71; AER, 24.03) and in the first 4 years of follow-up (SIR, 2.14; 95% CI, 1.03 to 3.94; AER, 12.24). Adjusted for age, the hazard ratio (brachytherapy v prostatectomy) for all SPCs combined was 0.87 (95% CI, 0.64 to 1.18). Conclusion Overall, we found no difference in SPC incidence between patients with prostate cancer treated with prostatectomy or brachytherapy. Furthermore, no increased tumor incidence was found compared with the general population. We observed a higher than expected incidence of bladder SPC after brachytherapy in the first 4 years of follow-up, probably resulting from lead time or screening bias. Because of power limitations, a small increased SPC risk cannot be formally excluded.