BACKGROUND: Currently, the 5-year survival rate for rectal cancer remains at <60%. The identification of potentially modifiable prognostic factors would be of considerable public health importance. A few studies have suggested associations between smoking and survival in rectal cancer; however, the evidence is inconsistent, and most of these studies were relatively small. In a large population-based cohort study, we investigated whether smoking at diagnosis is an independent prognostic factor for cancer-specific survival in rectal cancer and whether the association varies by sex, age, or treatment.
METHODS: Rectal cancers (ICD10 C19-20) diagnosed between 1994 and 2012 were abstracted from the National Cancer Registry Ireland and classified by smoking status at diagnosis. Follow-up was for 5 years or until December 31, 2012. Multivariable Cox proportional hazards models were used to compare cancer-specific death rates in current smokers, ex-smokers, and never smokers. Subgroup analyses by age at diagnosis, sex, and treatment were conducted.
RESULTS: A total of 10,794 rectal cancers were diagnosed. At diagnosis, 25% were current smokers, 24% were ex-smokers, and 51% were never smokers. Compared with never smokers, current smokers had a significantly greater rate of death from cancer (multivariable hazard ratio [HR], 1.15; 95% confidence interval [CI], 1.06-1.24), but ex-smokers did not (HR, 1.02; 95% CI, 0.94-1.11). The association was slightly stronger in men (current versus never smokers: HR = 1.13, 95% CI, 1.02-1.24) than females (HR, 1.05; 95% CI, 0.90-1.23), but the test for interaction was not significant (P = .75). The effect of smoking was not modified by age or receipt of tumor-directed surgery, radiotherapy, or chemotherapy.
CONCLUSIONS: Rectal cancer patients who smoke at diagnosis have a statistically significant increased cancer death rate. Elucidation of the underlying mechanisms is urgently required.
