Excessive risk of second primary cancers in young‐onset colorectal cancer survivors

With an increasing trend of patients with young‐onset colorectal cancer (CRC), risks of second primary cancers (SPCs) among them become a concerning issue. We aimed to define the detailed risk and site‐distributed patterns of SPCs in young CRC individuals (age ≤50). A population‐based cohort were identified from the Surveillance, Epidemiology, and End Results database between 1973 and 2013. Standardized incidence ratios (SIRs) and absolute excess risk (AER) were calculated to assess the risk for SPCs compared with the general population. A total of 44,106 patients, including 3245 (7.4%) the young and 40,861 (92.6%) the old, developed 50,679 secondary malignancies subsequently. With increased age, the risk of secondary cancers gradually decreased. A significant 44% excess risk of SPCs was observed in the young (SIR = 1.44, AER = 34.23), while a slightly increased risk was noted in the old (SIR = 1.02, AER = 4.29). For young survivors, the small intestine (SIR = 8.49), bile ducts (SIR = 3.77), corpus, and uterus (SIR = 2.45) were the most common sites of SPCs. Significantly, excess SIRs in the young were persisted regardless of other factors. For the young, secondary cancer‐related deaths were responsible for 51.2% of overall deaths and secondary stomach, liver and bile, pancreas cancers were top three causes. An excessive risk of SPCs existed in young CRC survivors, and this trend was consistent among different subgroups. We hope our findings may inform future targeted screening strategies among young‐onset CRC survivors.