Diet, lifestyle, and genomic instability in the north cancer study.

OBJECTIVE: Microsatellite instability (MSI) is one form of genomic instability that occurs in 10% to 20% of sporadic colon tumors and almost all hereditary nonpolyposis colon cancers. However, little is known about how environmental factors (e.g., diet) may influence MSI in sporadic colon cancer. METHODS: We used data from a population-based case-control study in North Carolina (486 colon cancer cases and 1,048 controls) to examine associations of diet (total energy, macronutrients, micronutrients, and food groups) with MSI. In-person interviews elicited information on potential colon cancer risk factors, and a previously validated food frequency questionnaire adapted to include regional foods was used to assess diet over the year before diagnosis or interview date. MSI was classified as MSI-high (MSI-H) and MSI-low or microsatellite stable (MSI-L/MSS). Multivariate logistic regression models estimated energy-adjusted and non-energy-adjusted odds ratios (OR). RESULTS: Ten percent of the cases (n = 49) had MSI-H tumors (29% African American). The strongest associations between diet and MSI were observed in case-control comparisons: there was a robust inverse association between MSI-H status and beta-carotene [OR, 0.4; 95% confidence interval (95% CI), 0.2-0.9] and positive associations with energy-adjusted refined carbohydrates (OR, 2.2; 95% CI, 0.9-5.4) and non-energy-adjusted read meat intake (OR, 2.0; 95% CI, 0.9-4.2). Compared with controls, MSI-L/MSS tumors were statistically significantly associated with energy-adjusted vitamin C, vitamin E, calcium, dietary fiber, and dark green vegetables and positively associated with total energy intake (all Ps for trend < 0.05). In case-case comparisons, no dietary factors were significantly differently related to MSI-H compared with MSI-L/MSS tumors. CONCLUSION: Refined carbohydrate and red meat consumption may promote development of MSI-H tumors, whereas beta-carotene may be associated with lower risk.