| Summary: | Background: Genetic and environmental factors have been associated with colorectal cancer (CRC) risk. However, their association with prognosis has been less studied.
Methods: Path analysis was employed to examine causal pathways from education to environmental (diet, alcohol, smoking, physical activity) and personal factors (screening), and then to obesity and ultimately to tumour characteristics (stage, grade, microsatellite instability (MSI), and site) that are associated with CRC prognosis. Data came from the Ontario Familial Colon Cancer Registry. Pathways were evaluated for effect modification by sex and two indicators of CRC genetic susceptibility (Bethesda criteria and newly identified familial cancer clusters).
Results: Four food patterns (healthy foods, high-fat foods, sweet and processed foods, and oriental foods) and four nutrient patterns (total macronutrient, fat vs. carbohydrate, and micronutrients from supplements and from foods) were identified. Education was associated positively with healthy lifestyle factors (e.g. healthy foods factor) and negatively with unhealthy factors (e.g. smoking). As expected, high body mass index (BMI) was associated with lower physical activity and higher fat vs. carbohydrate factor. Unexpectedly, BMI was positively associated with the healthy foods factor among Bethesda positive patients and men. An association between education and BMI was mediated by the healthy foods factor and by physical activity. Important poor prognostic factors, higher grade and stage, were associated with smoking and not being screened. However, unexpected associations included a positive association of physical activity with tumour grade among Bethesda positive patients and a positive association of healthy foods with stage among Bethesda negative patients. Patients with right-sided tumours were more likely to receive micronutrients from supplements, and screening and less likely to smoke, and for men, to have a high BMI, high fat diet and healthy food diet.
Conclusion: Some unhealthy lifestyle factors, such as smoking and a high fat food dietary pattern, are associated with adverse CRC tumour characteristics and so may affect the prognosis. Family history may modify some associations though the findings require independent confirmation.
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