Smoking habit and long-term colorectal cancer incidence by exome-wide mutational and neoantigen loads: evidence based on the prospective cohort incident-tumour biobank method.

Objective: To test the hypothesis that the association of smoking with long-term colorectal cancer incidence may be stronger for tumours with higher mutational and neoantigen loads.

Methods and analysis: In the Nurses' Health Study (1980-2012) and the Health Professionals Follow-up Study (1986-2012), our novel prospective cohort incident-tumour biobank method (PCIBM) used 3053 incident colorectal carcinoma cases including 752 cases with whole-exome sequencing data. Using the multivariable duplication-method Cox regression model with the inverse probability weighting to adjust for the selection bias due to tissue availability, we assessed a differential association of cigarette smoking with colorectal carcinoma incidence by an exome-wide tumour mutational burden (e-TMB) or neoantigen load.

Results: The association of pack-years smoked with colorectal cancer incidence differed by e-TMB (P_{heterogeneity}<0.001). Multivariable-adjusted HRs for e-TMB-high (≥10 mutations/megabase) tumours were 1.28 (95% CI 0.72 to 2.28) and 2.56 (95% CI 1.61 to 4.07) for 1-19 and ≥20 pack-years (vs 0 pack-years; P_trend<0.001), respectively. In contrast, pack-years smoked were not associated with e-TMB-low tumour incidence (P_trend=0.67). A similar differential association was observed for the neoantigen load (P_{heterogeneity}=0.017). The differential association by e-TMB appeared consistent in the strata of CpG island methylator phenotype status, BRAF mutation or lymphocytic infiltrates.

Conclusions: Smoking is more strongly associated with the long-term incidence of colorectal carcinoma harbouring higher mutational and neoantigen loads. Our PCIBM-based evidence supports the immunosuppressive effect of smoking and the potential of smoking cessation in improving antitumour immunity for cancer prevention and treatment.