Association between postoperative radiotherapy for bladder cancer and second primary rectal cancers:a retrospective cohort study
Objective To explore the association between postoperative radiotherapy for bladder cancer and the risk of second primary rectal cancer.Methods Eligible 75 120 patients with bladder cancer from the Surveillance,Epidemiology,and End Result database(SEER)of the National Cancer Institute(NCI)(1975-2017)were enrolled in this study.The second primary cancers referred to rectal cancers patients suffered after more than five years post-treatment for bladder cancer,and the cumulative incidence was estimated using Fine-Gray competing risk regression.The relative risk(RR)of rectal cancer in patients treated with or without radiotherapy(the RT group or the NRT group)was evaluated using Poisson regression.Results Among the 75 120 patients,70 045(92.4％)were Caucasian,with a median age of 65.8 years(54-74 years).A total of 2 236(3％)received postoperative radiotherapy,while 72 884(97％)received surgery alone.The 30-year follow-up revealed a cumulative incidence of rectal cancer of 0.93％in the RT group and 0.43％in the NRT group(P=0.004).The competing risk regression analysis identified a significant association between radiotherapy and rectal cancer(HR:1.86;95％CI 1.26-2.74,P＜0.009).Furthermore,the RR of radiotherapy-associated rectal cancer significantly increased as the diagnosis occurred earlier(1975-1985 vs.1985-1994:RR 2.59;95％Cl 1.20-4.86,P＜0.001),and a lower age at the time of radiotherapy was associated with a higher probability of second primary tumors(≤50-year old vs.＞50 year old:RR 7.89,95％CI2.97-21.30,P＜0.001).As calculated using the Poisson distribution,the RR of second rectal tumors was higher in the RT group(RR:2.20,95％CI 1.45-3.18,P＜0.001),even after adjusting the date of diagnosis(RR:1.77,95％CI 1.17-2.57,P=0.009).Conclusions An increased risk of rectal cancer following bladder cancer radiotherapy necessitates aggressive follow-ups for the purpose of early detecting second primary rectal cancer associated with bladder cancer radiotherapy.
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