A large meta-analysis found that current and former smoking status was associated with poorer colorectal cancer (CRC) prognosis compared with never smoking, and that smoking cessation may improve survival over those who continue to smoke.
“Current evidence on smoking and its association with prognosis after CRC diagnosis is still very limited due to the few available published studies, which are mainly from the US, and the heterogeneity in exposure and outcome assessment as well as in confounder adjustment across studies,” wrote investigators led by Viola Walter, PhD, MSc, of the German Cancer Research Center in Heidelberg.
The new analysis examined outcomes and correlations with smoking status in a total of 12,414 CRC patients, included in 14 cohort studies in 10 countries that participate in the CHANCES consortium. All patients were cancer-free before CRC diagnosis, the median age at diagnosis was 64.3 years, and there was a mean follow-up time of 5.1 years. The results were published online ahead of print in Annals of Oncology.
Among the full cohort of patients, 34% were never smokers, 49% were former smokers, and 16% were current smokers. During the follow-up period, a total of 5,229 patients died, and 3,194 died from CRC.
Compared with never smoking, former smokers had a hazard ratio (HR) for mortality of 1.12 (95% CI, 1.04–1.20); current smokers had an HR of 1.29 (95% CI, 1.04–1.60). Even after adjustments for covariates, having stopped smoking both less than 10 years ago (HR, 0.78; 95% CI, 0.69–0.88) and 10 or more years ago (HR, 0.78; 95% CI, 0.63–0.97) were significantly associated with improved survival outcomes.
With regard to CRC-specific survival, a significant association was seen in patients who stopped smoking 10 or more years earlier compared with current smokers, with an HR of 0.76 (95% CI, 0.67–0.85). No such association was seen for those who stopped smoking less than 10 years earlier. Results regarding cessation and outcomes were similar in nonmetastatic patients only.
“Smoking is a well-known risk factor for many adverse health outcomes including CRC and its precursors,” the authors wrote. “In this large meta-analysis examining the association between smoking and CRC prognosis, former as well as current smoking were associated with poorer overall survival…. Future studies should further quantify the benefits of not smoking, both for cancer prevention and for improving survival among CRC patients, in particular also in terms of interactions between smoking and treatment response.”