Study Links High BMI Before Diagnosis to Increased Death Risk in Colorectal Cancer

Peter T. Campbell, PhD

Patients who had a high Body Mass Index (BMI) before being diagnosed with colorectal cancer had an increased risk of death after diagnosis, even if their tumor harbored the microsatellite instability (MSI) marker, which is normally associated with a better prognosis, according to results of a large prospective study presented at the 2014 Annual AACR Meeting.

“Our study, to our 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,” Peter T. Campbell, PhD, director of the Tumor Repository in the Epidemiology Research Program at the American Cancer Society in Atlanta said in a press release. “Colorectal cancer patients with tumors with the MSI-high characteristic have a better prognosis than patients with tumors lacking this feature. How obesity, as defined by a high BMI, influences survival of colorectal cancer patients has not been clearly determined.”

The study identified 6763 patients with invasive colorectal cancer among participants who enrolled in the Colon Cancer Family Registry from 1997 to 2008. Researchers calculated the patients’ BMI 2 years prior to diagnosis based on self-reports of height and weight. MSI tumor status was available for 4987 patients and the median follow-up was 5.3 years, according to the study.

BMI is calculated as weight in kilograms (kg) divided by height in meters squared (m²). In adults, a BMI of 30 or more kg per m² is considered obese.

“Our data provide further evidence that maintaining a healthy body weight throughout life is very important,” Campbell continued. “They also suggest that prediagnosis BMI may be something that clinicians should consider when managing patient care.”

After a maximum follow-up of 13.7 years from enrollment-end of study, it was found that 2335 patients had died. For colorectal cancer-specific—mortality, every 5 kg per m² increase in BMI increased mortality by 7%. In patients with MSI-high tumors, every 5 kg per m² increase in BMI increased the risk of all-cause mortality by 19%, while patients with MSI-stable/MSI-low saw an increase of 8%.

Results showed that a higher BMI 2 years before a general cancer diagnosis (per 5-kg/m²) was associated with higher risk of all-cause mortality overall (HR = 1.10; 95% CI, 1.05 to 1.14). For every 5 kg per m² increase in BMI, researchers saw an increased risk of all-cause mortality by 10%.

“Now that we have seen that obesity attenuates the survival advantage observed for patients with MSI-high tumors, we are looking at how it affects other tumor markers that have relevance for colorectal cancer survival,” said Campbell. “Ultimately, we would like to investigate associations between obesity and somatic tumor mutations to see if we can figure out how obesity drives cancer.”