Smoking status and prognosis in patients with stage III colon cancer: A correlative analysis of NCCTG phase III trial N0147.

Abstract

3526 Background: Prior observational studies have suggested that smoking is associated with poorer overall survival after colon cancer (CC) diagnosis. Using data from N0147, a phase III randomized adjuvant trial of patients with stage III CC, we assessed the relationship between smoking status and cancer outcomes (disease-free survival (DFS) and time to recurrence (TTR)), accounting for possible heterogeneity by patient and tumor characteristics. Methods: Patients completed a risk factor questionnaire at baseline prior to randomization to FOLFOX or FOLFOX+cetuximab (N=1968). Information was collected on smoking and other lifestyle factors, including alcohol consumption, body mass index (BMI), and physical activity. Multivariate Cox models assessed the association between smoking history and the primary trial outcome of DFS, as well TTR, adjusting for other lifestyle and clinical factors. The median follow-up was 3.5 years. Results: Overall, 52% of patients were former or current smokers. Compared to never smokers, ever smokers experienced significantly shorter DFS [3-year DFS: 70% vs 74%, hazard ratio (HR)=1.21, 95% confidence interval (CI): 1.02-1.42]. This association persisted after adjusting for age, sex, tumor subsite, number of nodes involved, T-stage, mismatch repair deficiency, BRAF mutation status, performance score, physical activity, BMI, and alcohol consumption (HR=1.23, 95% CI: 1.02-1.49). There was significant interaction in this association by BRAF mutation status (p=0.02): smoking was associated with shorter DFS in BRAF wildtype CC patients (HR=1.25, 95% CI: 1.04-1.51) but not in BRAF mutant CC patients (HR=0.72, 95% CI: 0.47-1.10). Patterns of association with smoking, overall and by BRAF status, were identical in analyses of TTR. Conclusions: Overall, smoking was significantly associated with shorter DFS and TTR in CC patients. These adverse relationships were most evident in patients with BRAF wildtype CC.