Patients with Early-Onset Colorectal Cancer Have an Increased Risk of Second Primary Malignancy

While overall colorectal cancer (CRC) rates in the USA are declining, the incidence of early-onset CRC (eoCRC) under age 50 is increasing. The aim of this study was to examine the risk of a second primary malignancy (SPM) in individuals with eoCRC, and how this risk compares to those with late-onset CRC (loCRC).

We used data from the Surveillance, Epidemiology, and End Results Program database to examine the risk of SPM after a diagnosis of eoCRC. Standardized incidence ratios (SIR) were used to estimate the risk of SPM after eoCRC and loCRC in comparison with the risk of malignancy in the general population.

Compared to the general population, individuals with eoCRC, but not loCRC, had an increased lifetime risk of SPM (SIR 1.42, 95% CI 1.37-1.48 and SIR 1.00, 95% CI 0.99-1.02, respectively), and locations at highest risk were the small intestine, ureter, rectum, and colon. The risk of SPM after eoCRC was similar in men and women, but higher in non-whites compared to whites and higher in those with a lower area-level median household income. The risk of SPM following eoCRC was high in the first 5 years after diagnosis (SIR 2.44, 95% CI 2.24-2.66) and, in a birth cohort analysis, was found to be increasing over time.

Individuals with eoCRC have a lifetime risk of SPM nearly 50% higher than the general population. The risk of SPM is highest in the first 5 years after diagnosis and is increasing over time.