Prediagnostic Obesity Curbs Colorectal Cancer Survival

Peter T. Campbell, PhD

Patients who are obese before being diagnosed with colorectal cancer are more likely to die of their disease than patients who are at a normal weight prediagnosis, according to the results of a large prospective study.

Peter T. Campbell, PhD, with the Epidemiology Research Program at the American Cancer Society in Atlanta, Georgia, and colleagues examined the association of pre- and postdiagnosis body mass index (BMI) with all-cause and cause-specific survival in 2303 men and women from the prospective Cancer Prevention Study-II (CPS-II) Nutrition Cohort who were diagnosed with nonmetastatic colorectal cancer.

The CPS-II Nutrition Cohort is a prospective study of cancer incidence in which participants completed a questionnaire at enrollment in 1992 and 1993 that sought information on demographics, medical history, body weight, physical activity, cigarette smoking, diet, and other lifestyle factors. Patients were also asked to respond to repeat questionnaires at multiple time points to provide updated information on weight and incident cancer.

Given that there are more than 1.1 million colorectal cancer survivors in the United States, it is important to identify factors that affect colorectal cancer survivors, Campbell and colleagues said. The only established prognostic factors for colorectal cancer are tumor characteristics, including tumor stage and grade, nodal involvement, and the presence of distant metastasis. Little is known about the prognostic role of factors such as BMI, which has important clinical and public health significance.

A total of 851 participants with colorectal cancer died during the 16-year follow-up period, including 380 deaths due to colorectal cancer and 153 deaths due to cardiovascular disease (CVD).

The investigators analyzed prediagnosis BMI at a mean of 7 years before patients were diagnosed with colorectal cancer, and found that obese BMI relative to normal was associated with a higher risk of all-cause mortality (relative risk [RR], 1.30; 95% CI, 1.06-1.58), colorectal cancer (RR, 1.35; 95% CI, 1.01-1.80), and CVD (RR, 1.68; 95% CI, 1.07-2.65). Obesity was defined as a BMI ≥ 30 kg/m2, and normal weight was defined as a BMI from 18.5 to 24.9 kg/m2.

The association between BMI and all-cause mortality was stronger for patients diagnosed with rectal cancer than those for those diagnosed with colon cancer. There were no associations of postdiagnosis obese BMI, which was reported a mean of 18 months after colorectal cancer diagnosis, with all-cause or cause-specific mortality.

Campbell and colleagues said that the mechanisms by which obesity influences colorectal cancer prognosis are not well defined and may include biologic mechanisms that are associated with colorectal cancer incidence, including insulin and insulin-like growth factors, among others.

The authors cite the ability to examine both pre- and postdiagnosis reports of BMI as an important study strength, along with its relatively large sample size, prospective design, and the inclusion of detailed information on key confounders.

Campbell PT, Newton CC, Dehal AN, et al. Impact of body mass index on survival after colorectal cancer diagnosis: The Cancer Prevention Study-II Nutrition Cohort [published online ahead of print November 28, 2011]. J Clin Oncol. 2012;30(1):42-52.