Lynch syndrome family members with inherited germline mutations in DNA mismatch repair (MMR) genes have a high risk of colorectal cancer (CRC) and cases typically have tumors that exhibit a high level of microsatellite instability (MSI). There is some evidence that smoking is a risk factor for CRCs with high MSI, but the association of smoking with CRC among those with Lynch syndrome is unknown.
A multicentered retrospective cohort of 752 carriers of pathogenic MMR gene mutations was analyzed, using a weighted Cox regression analysis, adjusting for sex, ascertainment source, the specific mutated gene, year of birth, and familial clustering.
Compared with never smokers, current smokers had a significantly increased CRC risk (adjusted hazard ratio [HR] = 1.62; 95% CI, 1.01 – 2.57) and former smokers who had quit smoking for 2 or more years were at decreased risk (HR = 0.53; 95% CI, 0.35 – 0.82). CRC risk did not vary according to age at starting. However, light smoking (<10 cigarettes per day) and shorter duration of smoking (<10 years) were associated with decreased CRC risk (HR = 0.51; 95% CI, 0.29 – 0.91 and HR = 0.52; 95% CI, 0.30 - 0.89 respectively). For former smokers, CRC risk decreased with years since quitting (P trend <0.01).
People with Lynch syndrome may be at increased risk of CRC if they smoke regularly. Although our data suggest that former smokers, short-term and light smokers are at decreased CRC risk, these findings need further confirmation, preferably using prospective designs.