Effect of physical activity and body size on survival after diagnosis with colorectal cancer

Background: Physical inactivity and obesity increase the risk of colorectal cancer but little is known about whether they influence prognosis after diagnosis. Methods: Incident cases of colorectal cancer were identified among participants of the Melbourne Collaborative Cohort Study, a prospective cohort study of 41 528 Australians recruited from 1990 to 1994. Participants diagnosed with their first colorectal cancer between recruitment and 1 August 2002 were eligible. At the time of study entry, body measurements were taken and participants were interviewed about their physical activity. Information on tumour site and stage, treatments given, recurrences, and deaths were obtained from systematic review of the medical records. Results: A total of 526 cases of colorectal cancer were identified. Median follow up among survivors was 5.5 years, and 208 deaths had occurred, including 181 from colorectal cancer. After adjusting for age, sex, and tumour stage, exercisers had an improved disease specific survival ( hazard ratio 0.73 ( 95% confidence interval (CI) 0.54 - 1.00)). The benefit of exercise was largely confined to stage II - III tumours ( hazard ratio 0.49 ( 95% CI 0.30 - 0.79)). Increasing per cent body fat resulted in an increase in disease specific deaths ( hazard ratio 1.33 per 10 kg ( 95% CI 1.04 - 1.71)). Similarly, increasing waist circumference reduced disease specific survival ( hazard ratio 1.20 per 10 cm ( 95% CI 1.05 - 1.37)). Conclusions: Increased central adiposity and a lack of regular physical activity prior to the diagnosis of colorectal cancer is associated with poorer overall and disease specific survival.