The incidence of secondary pelvic tumors after previous (chemo)radiation for rectal cancer.

491 Background: The aim of this study was to analyze the association between radiotherapy (RT) for rectal cancer and the development of second primary tumors. Methods: Data on all surgically treated, non-metastasized primary rectal cancer patients diagnosed between 1989 and 2007 were retrieved from a population-based cancer registry and retrospectively reviewed. To estimate the cumulative incidence of a second tumor, Fine and Gray’s competing risk model was used with death as a competing event. Standardized incidence ratios (SIR’s) were calculated for comparison with the incidence of primary tumors in the general population, taking in account sex, age and calendar year. Results: The cohort consisted of 29,214 patients of which 15,454 patients had undergone (chemo)RT. Median follow-up was 6.2 years (range 0-24). 3655 patients were diagnosed with at least one second primary tumor of which 808 patients had pelvic tumors. The SIR for any second tumor was 1.14 (95% confidence interval [CI] 1.10-1.17), resultin...