Metachronous colorectal cancer risk in patients with a moderate family history

Aim Lifetime risk of a metachronous colorectal cancer (mCRC) is 0.6–3% following sporadic colorectal cancer (CRC) and 15–26% in Lynch syndrome. The lifetime incidence of CRC in individuals with moderate familial risk is 8–17%. Risk of mCRC is unknown. Method A retrospective longitudinal study of the Regional Familial CRC Registry was performed. Patients who had at least one CRC were categorized as follows: moderate risk (n = 383), Lynch syndrome (n = 528) and average (population) risk (n = 409). The Kaplan–Meier estimate (1‐KM) and the cumulative incidence function were used to calculate the risk of mCRC. The 1‐KM gives the risk for individuals remaining at risk (alive) at a given time point and thus is useful for counselling. The cumulative incidence function gives the risk for the whole population. Results The 1‐KM and the cumulative incidence function demonstrated that the risk of mCRC was significantly higher in moderate‐risk patients compared with average (population)‐risk patients (1‐KM, P = 0.008; cumulative incidence function, P = 0.00097). However, the risk of mCRC was higher in patients with Lynch syndrome than in moderate‐risk or average (population)‐risk patients. The 1‐KM in moderate‐risk patients was 2.7%, 6.3% and 23.5% at 5, 10 and 20 years, respectively. In average (population)‐risk patients, the 1‐KM was 1.3%, 3.1% and 7.0% at 5, 10 and 20 years, and the cumulative incidence function was 0.3%, 0.6% and 2.4% at the same time points, respectively. Conclusion These data indicate that the risk of mCRC is significantly higher in patients with a moderate family history of CRC than in those with an average (population) risk. This justifies proactive lifelong surveillance.