Active smoking may increase mortality among colorectal cancer survivors

1. In a prospective cohort of over 2,500 patients diagnosed with non-metastatic colorectal cancer, post-diagnosis active smoking was associated with a significant increase in cancer-specific and all-cause mortality.

2. Post-diagnosis former smokers were associated with an increase in all-cause mortality, but with no increased risk of cancer-specific mortality.

Evidence Rating Level: 2 (Good)

Study Rundown: Smoking exposure has been recently attributed to an increased risk of colorectal cancer (CRC). However, the effect of smoking exposure after the diagnosis of CRC on patient survival is unclear. The purpose of this study was to evaluate the association between pre- and post-diagnosis smoking and mortality among patients with non-metastatic CRC. The study prospectively followed over 2,500 patients with localized or regional CRC for vital status and cause of death. Smoking status was determined by self-reported questionnaires. At the conclusion of this trial, post-diagnosis active smoking was associated with a higher all-cause and cancer specific mortality compared to non-smokers. Post-diagnosis former smokers were associated with an increase in all-cause mortality, but not cancer-specific mortality compared to non-smokers. The same pattern was observed in pre-diagnosis active and former smokers. The results of this study support the conclusion of a significant increase in mortality risk of smoking exposure for CRC cancer survivors. However, the study is limited by the lack of information on the treatment efficacy of these patients. Furthermore, given that smoking exposure is shown to be related to CRC of specific genetic genotypes, additional prospective trials with a focus on these correlated genotypes would clarify this association.

Click to read the study in JCO

Relevant Reading: A review of human carcinogens—Part E: tobacco, areca nut, alcohol, coal smoke, and salted fish

In-Depth [prospective cohort]: This prospective trial included 2,548 patients (1,416 male and 1,132 female) with localized or regional, non-metastatic CRC from the Cancer Prevention Study II (CPS-II) nutrition cohort. All patients were free of disease at the time of enrollment. The average age at diagnosis was 73 years. The primary outcomes were all-cause and colorectal cancer-specific mortality. Smoking exposure was determined by self-reported questionnaire as never smokers, former smokers, or active smokers. Following Cox proportional hazard regression analysis, pre-diagnosis current smoking was associated with higher all-cause mortality (RR: 2.12; 95% CI: 1.65 to 2.74) and CRC–specific mortality (RR: 2.14; 95% CI: 1.50 to 3.07) compared to non-smokers, whereas former smoking was associated with only higher all-cause mortality (RR: 1.18; 95% CI: 1.02 to 1.36). Similarly, post-diagnosis current smoking was associated with higher all-cause (RR: 2.22; 95% CI: 1.58 to 3.13) and colorectal cancer–specific mortality (RR: 1.92; 95% CI: 1.15 to 3.21). Post-diagnosis former smoking was associated with only increases in all-cause mortality (RR: 1.21; 95% CI: 1.03 to 1.42), but not CRC-specific mortality (RR: 0.91; 95% CI: 0.71 to 1.18).

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