Background: Marine w-3 polyunsaturated fatty acids (PUFAs), primarily found in dark fish, may prevent colorectal cancer progression, in part through inhibition of prostaglandin-endoperoxide synthase 2 (PTGS2). However, data in humans are limited. Methods: We examined marine w-3 PUFAs and fish intake and survival among 1,011 colon cancer patients enrolled in Cancer and Leukemia Group B 89803 between 1999 and 2001 and followed through 2009. Diet was assessed during and 6 months after chemotherapy. We used Cox proportional hazards regression to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for disease-free (DFS), recurrence-free (RFS), and overall survival (OS). Results: We observed 343 recurrences and 305 deaths (median follow-up: 7 years). Patients in the highest vs. lowest quartile of marine w-3 PUFA intake had an HR for DFS of 0.72 (95% CI, 0.54–0.97; Ptrend ¼ 0.03). Individuals who consumed dark fish 1/week versus never had longer DFS (HR 0.65; 95% CI, 0.48–0.87; P-value ¼ 0.007), RFS (HR 0.61; 95% CI, 0.46–0.86; Ptrend ¼ 0.007), and OS (HR 0.68; 95% CI, 0.48–0.96; Ptrend ¼ 0.04). In a subset of 510 patients, the association between marine w-3 PUFA intake and DFS appeared stronger in patients with high PTGS2 expression (HR 0.32; 95% CI, 0.11–0.95; Ptrend ¼ 0.01) compared with patients with absent/low PTGS2 expression (HR 0.78; 95% CI, 0.48–1.27; Ptrend ¼ 0.35; Pinteraction ¼ 0.19). Conclusions: Patients with high intake of marine w-3 PUFAs and dark fish after colon cancer diagnosis may have longer DFS.
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