Background: Although several studies have established a link between obesity and colon cancer risk, little is known about the effect of obesity on outcomes after diagnosis. We investigated the association of body mass index (BMI) with outcomes after colon cancer in patients from cooperative group clinical trials.
Methods: The study cohort consisted of 4288 patients with Dukes B and C colon cancer who were accrued from July 1989 to February 1994 to National Surgical Adjuvant Breast and Bowel Project randomized trials. Risk of recurrence, second primary cancer, and mortality (overall and by likely cause) were evaluated in relation to BMI at diagnosis using statistical modeling. Median follow-up time was 11.2 years. All statistical tests were two-sided.
Results: Very obese patients (BMI > or = 35 kg/m2) had greater risk of a colon cancer event (recurrence or secondary primary tumor; hazard ratio [HR] = 1.38, 95% confidence interval [CI] = 1.10 to 1.73) than normal weight patients (BMI = 18.5-24.9 kg/m2). Mortality was greater for very obese (HR = 1.28, 95% CI = 1.04 to 1.57) and underweight (BMI < 18.5 kg/m2) (HR = 1.49, 95% CI = 1.17 to 1.91) than for normal weight patients. The increased risk of mortality for underweight patients was dominated by non-colon cancer deaths (HR of such deaths compared with normal weight patients = 2.23, 95% CI = 1.50 to 3.31), whereas for the very obese, deaths likely due to colon cancer were increased (HR = 1.36, 95% CI = 1.06 to 1.73).
Conclusions: Among colon cancer patients, a BMI greater than 35.0 kg/m2 at diagnosis was associated with an increased risk for recurrence of and death from colon cancer. Further studies are needed to determine pathways between obesity and recurrence risk and whether weight reduction or related interventions would improve prognosis.