Yet another study points out the dangers of obesity, in this case the relationship of prediagnosis obesity to poor outcomes for people with colorectal cancer. In fact, the presence of prediagnosis obesity trumped high microsatellite instability (MSI), a tumor marker usually associated with better outcomes.
“We know that increased body mass index [BMI] is associated with a variety of poor health outcomes, including poor prognosis in survivors of breast and endometrial cancers. One of the clearest associations is with colorectal cancers. The timing of obesity is important, because increased BMI measured before diagnosis is predictive. After diagnosis, BMI is no longer predictive because patients get sick and lose weight,” explained lead author Peter T. Campbell, PhD, director of the Tumor Repository in the Epidemiology Research Program at the American Cancer Society in Atlanta, Georgia.
“This study, to my knowledge, is the first study with sufficient numbers to investigate how these independent risk factors work together to influence survival after a colorectal cancer diagnosis. We found that a high prediagnosis BMI is associated with increased all-cause and colorectal cancer–specific mortality after diagnosis. We also found that high BMI overrides the survival advantage conferred by an MSI-high tumor,” he said.
“The take-home message is that BMI is prognostic. At the highest level (BMI >40 kg/m2), colorectal cancer mortality was increased by 48%. This is another reason to maintain lower body weight,” Campbell stated.
The study was based on 6763 patients with invasive colorectal cancer who enrolled in the Colon Cancer Family Registry from 1997 to 2008. BMI 2 years prior to diagnosis and at age 20 years and adult weight gain were calculated from self-reports of height and weight. Tumor MSI status was available for 4987 patients. Median follow-up was 5.3 years.
For every 5 kg/m2 increase in BMI, there was a 10% increase in all-cause mortality. For patients with MSI-high and MSI-stable/MSI-low tumors, every 5 kg/m2 increase in BMI increased all-cause mortality by 19% and 8%, respectively.
A similar pattern was observed for the association between increased BMI and colorectal cancer–specific mortality as well, with the risk of colorectal cancer–specific mortality increasing by 7% for every 5 kg/m2 increase in BMI.
“This study is unique because we looked at the joint impact of BMI and MSI. Obesity removes the net benefit of high MSI,” Campbell emphasized.
He and his colleagues are planning to look at the association between prediagnosis obesity and other tumor markers implicated in colorectal cancer survival. The ultimate goal is to investigate the association between obesity and somatic tumor mutations to determine how obesity may drive cancer, he noted.
Campbell PT, Newton C, Newcomb PA, et al. Prospective study of body mass index and adult weight change with colorectal cancer survival, overall and by tumor microsatellite instability status. Presented at: 2014 Annual Meeting of the American Association for Cancer Research; April 5-9, 2014; San Diego, CA. Abstract LB-276.