Extremes of BMI linked to poorer colorectal cancer outcomes

Last Updated: 2016-05-25

By Larry Hand

NEW YORK (Reuters Health) - Extremes in weight in individuals at the time of diagnosis of colorectal cancer are associated with an increased risk of death, while those who are overweight may live longer, according to a new study.

"In the immediate time period following a diagnosis of colorectal cancer, patients should not be encouraged to lose weight if overweight. Rather, weight maintenance and encouragement of physical activity are better goals," Dr. Candyce H. Kroenke of Kaiser Permanente in Oakland, California, told Reuters Health by email.

Dr. Kroenke and colleagues conducted a retrospective study with prospectively collected data on more than 3,400 men and women 18 to 80 years old in the Kaiser Permanente Northern California population diagnosed with stage I - III colorectal cancer between 2006 and 2011.

The team evaluated the association between body mass index (BMI) at the time of diagnosis and following diagnosis of colorectal cancer and mortality. All study participants had surgery.

During a median follow-up of 4.5 years, 617 patients died. Among those included in analyses of post-diagnosis BMI and mortality, 482 of 3,157 patients died during a median follow-up of 3.5 years, the researchers report in JAMA Oncology, online May 19.

Adjusting for age, sex, and race, the researchers found BMI at diagnosis to be associated with mortality in a nonlinear way. Underweight patients (BMI less than 18.5) and class II and II obese patients (BMI 35 or greater) had higher all-cause mortality risks, compared with overweight patients (BMI 25 to less than 30) and normal-weight patients (BMI 18.5 to less than 25). However, the association for class II and III obese was no longer statistically significant after adjusting for comorbidity.

The researchers found that all-cause mortality was lowest in men and women patients with a BMI of 28.

Associations for colorectal cancer-specific mortality were similar to those for all-cause mortality, and the researchers found few differences by age, race, sex, stage, comorbidity, treatment, or weight-loss status.

"In the context of disease, being overweight may confer survival benefits, attributed to better nutritional status, more optimal medical treatment, greater endothelial progenitor cells, lower thromboxane production, higher ghrelin sensitivity, and lower concentrations of tumor necrosis factor-(alpha)," the researchers write. "Patients with (colorectal cancer) with extra weight may have greater muscle and fat mass enabling them to cope with the metabolic demands of tumor progression and treatment."

Body composition could be a factor also, Dr. Kroenke said. "There have been a number of methodologic issues that have been raised, but we believe that research into body composition is an important next step."

In an accompanying editorial, Drs. Andrew W. Renehan and Matthew Sperrin, of the University of Manchester, U.K., note that the "obesity paradox is well recognized in the cardiovascular and metabolic literature and is now being recognized in oncology, for example, after surgery for clear-cell renal carcinoma and in a population-level study of mortality after colorectal cancer diagnosis."

"The observations of Kroenke et al might be paradoxical, but they are readily explained through several methodologic mechanisms. These findings should not alter current clinical practice or recommendations," they conclude.

SOURCE: http://bit.ly/1U4bFJq and http://bit.ly/1XFaPpE

JAMA Oncol 2016.