Influence of prediagnostic dietary patterns and cigarette smoking on colorectal cancer survival: a cohort study

Cigarette smoking and dietary patterns are associated with colorectal cancer (CRC) incidence; however, little is known about their influence on survival after CRC diagnosis. This study was designed to: 1) investigate the association of dietary patterns with all-cause (overall survival; OS) and disease-free survival (DFS) among CRC patients; 2) examine the association of smoking with OS and DFS among CRC patients. A cohort of 750 CRC patients diagnosed from 1999 to 2003 in the Canadian province of Newfoundland and Labrador was followed for mortality and recurrence until April 2010. Participants reported their smoking history and dietary intakes using a personal history questionnaire and a food frequency questionnaire. Dietary patterns were identified with factor analysis. Multivariate hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated with Cox proportional hazards regression, controlling for major known prognostic factors. Results from this study are presented in two parts: 1) Disease-free survival among CRC patients was significantly worsened among patients with a high dietary intake of processed meat (the highest versus the lowest quartile HR: 1.82, 95%CI: 1.07-3.09). No associations were observed with the prudent vegetable or the high sugar patterns and DFS. The association between the processed meat pattern and survival in CRC patients was restricted to patients diagnosed with colon cancer (the highest versus the lowest quartile: DFS: HR: 2.29, 95%CI: 1.19-4.40; OS: HR: 2.13, 95%CI: 1.03-4.43). Potential effect modification was noted for sex (DFS: P=0.04, HR: 3.85 for women and 1.22 for men). 2) Compared with never smoking, current (HR: 1.78; 95%CI: 1.04-3.06), but not former (HR: 1.06; 95%CI: 0.71-1.59), smoking was associated with decreased OS, although this association was limited to tumors in the colon. The associations of cigarette smoking with the study outcomes were higher among patients with >40 pack-years of smoking (OS: HR: 1.72; 95%CI: 1.03-2.85; DFS: HR: 1.99; 95%CI: 1.25-3.19). Potential interaction was noted for sex (DFS: P=0.04, HR: 1.68 for men and 1.01 for women) and age at diagnosis (OS: P=0.03, HR: 1.11 for patients aged < 60 and 1.69 for patients aged 60). In summary, 1) processed meat dietary pattern prior to diagnosis is associated with higher risk of tumor recurrence, metastasis, or death from any cause among colon cancer patients; 2) pre-diagnosis cigarette smoking is associated with worsened prognosis among patients with colon cancer