A high body mass index (BMI) prior to a colorectal cancer diagnosis is linked to a higher risk of death, even when the patient’s tumor type is generally associated with a better prognosis.
A higher BMI (weight in kilograms divided by height in m2) 2 years prior to diagnosis increased the risk of all-cause mortality after a colorectal cancer diagnosis. For every 5 kg/m2 increase in BMI, risk of all-cause mortality increased by 10%. Colon cancer-specific mortality increased by 7% for every 5 kg/m2 increase in BMI. Similar risk was seen for both men and women.
Results from a large, prospective study were presented at the annual meeting of the American Association of Cancer Research (AACR) by Peter T. Campbell, PhD, who directs the tumor repository in the epidemiology research program at the American Cancer Society in Atlanta.
“Our study, to our knowledge, is the first with sufficient numbers to investigate how these independent risk factors work together to influence survival after a colorectal cancer diagnosis,” said Campbell in a released statement.
A high BMI conferred a higher risk of colorectal cancer mortality even in patients with tumors that harbor the microsatellite instability (MSI) marker, a marker that is typically associated with a better prognosis in colorectal cancer. Information on MSI status was available for 65% of patients in this study.
Patients with MSI-high and MSI-stable/MSI-low tumors had a 19% and 8% increase in all-cause mortality for every 5 kg/m2 increase in BMI, respectively.
Obesity is defined as a BMI of 30 kg/m2 or greater.
The researchers analyzed 6,763 patients with colorectal cancer who were part of the Colon Cancer Family Registry from 1997 to 2008 and were followed up for a median of 5.3 years. Self-reported weight and height information from age 20 until colorectal cancer diagnosis was used to calculate each patient’s BMI.
After a maximum of 13.7 years of follow-up, 2,335 of the patients had died.
Prior studies have indicated that obesity, as assessed by BMI, increases the risk of colorectal cancer. The current research literature along with this study underscores the benefits of maintaining a healthy weight—to both lower one’s risk of colorectal cancer and also lower the chances of dying from colorectal cancer after diagnosis.
Campbell and colleagues are now looking into the mechanisms of how obesity may affect colorectal cancer progression in patients with MSI-high tumors, particularly the associations of obesity and somatic tumor mutations that drive colorectal cancer.
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. American Association for Cancer Research Annual Meeting 2014; April 5–9, 2014; San Diego. Abstr LB-276.