Second primary cancer among 217702 colorectal cancer survivors: An analysis of national German cancer registry data

With improvements in survival after colorectal cancer (CRC), more survivors are at risk of developing a second cancer, particularly in younger populations where CRC incidence is increasing. We estimated the incidence of second primary cancer (SPC) in CRC survivors and its potential risk factors. We identified CRC cases diagnosed between 1990 and 2011 and SPCs until 2013 from nine German cancer registries. Standardized incidence ratios (SIR) and absolute excess risk (AER) per 10 000 person-years were calculated and were stratified by index site: colon cancer (CC) and rectal cancer (RC), age and sex. Cox regression assessed potential SPC risk factors, including primary tumor-related therapy considering death as a competing risk. We included 217 202 primary CRC cases. SPC occurred in 18 751 CRC survivors (8.6%; median age: 69 years). Risk of cancer was significantly higher in CRC survivors than in the general population (SIR males 1.14, 95% confidence interval [CI] 1.12-1.17, AER = 24.7; SIR females 1.20, 95% CI 1.17-1.23, AER = 22.8). Increased risks of SPCs were observed for the digestive system, urinary system and female and male reproductive organs. CRC incidence increased in younger persons (<50 years) and SPC incidence was 4-fold in this group (SIR males 4.51, 95% CI 4.04-5.01, AER = 64.2; SIR females 4.03, 95% CI 3.62-4.48, AER = 77.0). Primary tumor-related factors associated with SPC risk were right-sided cancer and smaller primary tumor size. Treatment and risk of SPC differed for CC (no effect) and RC (lower risk after chemotherapy). CRC survivors have excess risk of developing SPC, with particular characteristics that could guide targeted surveillance.