Smoking and survival of colorectal cancer patients: systematic review and meta-analysis

Smoking is a risk factor for colorectal cancer (CRC) incidence and mortality. However, little is known on smoking and its association with survival after CRC diagnosis. We conducted a systematic review and meta-analysis to summarize current evidence. A systematic literature search was carried out in MEDLINE and ISI Web of Science. We included studies that analyzed recurrence-free survival, disease-free survival, all-cause, and CRC-specific mortality according to smoking status. Data were extracted in duplicate. Standard methods of meta-analysis were applied. Sixteen studies from 11 countries were identified, comprising a total sample size of 62 278 CRC patients. Overall, in the 16 included studies, current smoking and, to a lesser extent, former smoking were rather consistently associated with a poorer prognosis compared with never smokers. Meta-analyses yielded random-effects hazard ratio estimates (95% confidence intervals) for all-cause mortality of 1.26 (1.15-1.37) and 1.11 (0.93-1.33) for current and former smokers, compared with never smokers, respectively. In particular, 30-day mortality was found to be increased by between 49% and 100% among current compared with never smokers. Our results support the existence of detrimental effects of smoking on survival also after CRC diagnosis. Perspectives for enhancing prognosis of CRC patients by smoking abstinence deserve increased attention in further research and clinical practice.