High body mass index (BMI), an indicator of obesity, before a colorectal cancer diagnosis was associated with increased risk of death after diagnosis, and this was seen even when tumours harboured the microsatellite instability (MSI) marker normally associated with better prognosis, according to results of a large prospective study presented at the AACR Annual 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,” said Peter T. Campbell, Ph.D., director of the Tumour Repository in the Epidemiology Research Program at the American Cancer Society in Atlanta.

“Colorectal cancer patients with tumours with the MSI-high characteristic have a better prognosis than patients with tumours lacking this feature. How obesity, as defined by a high BMI, influences survival of colorectal cancer patients has not been clearly determined.

“We found that a high prediagnosis BMI is associated with increased all-cause and colorectal- cancer specific mortality after diagnosis,” Campbell said.

“We also found that high BMI overrides the survival advantage conferred on patients by an MSI-high tumour.

“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.”

BMI is calculated as weight in kilogrammes (kg) divided by height in metres squared (m2).

It is used to define healthy weight, overweight, and obesity.

In adults, a BMI of 30 or more kg per m2 is considered obese.

Campbell and colleagues identified 6,763 patients with invasive colorectal cancer among participants who enrolled in the Colon Cancer Family Registry from 1997 to 2008.

BMI two years before diagnosis was calculated from self-reports of height and weight.

Tumour MSI status was available for 4,987 patients.

Median follow-up was 5.3 years.

The researchers found that higher BMI two years before diagnosis increased risk of all-cause mortality after diagnosis: Every 5 kg per m2 increase in BMI increased risk of all-cause mortality by 10 percent.

Similar associations were seen for patients with MSI-high and MSI-stable/MSI-low tumours: Every 5 kg per m2 increase in BMI increased risk of all-cause mortality by 19 percent and 8 percent, respectively.

According to Campbell, similar patterns of association were seen for colorectal cancer-specific mortality: Every 5 kg per m2 increase in BMI increased risk of colorectal-cancer specific mortality by 7 percent.


“Now that we have seen that obesity attenuates the survival advantage observed for patients with MSI-high tumours, we are looking at how it affects other tumour markers that have relevance for colorectal cancer survival,” said Campbell.

“Ultimately, we would like to investigate associations between obesity and somatic tumour mutations to see if we can figure out how obesity drives cancer.”

Source: AACR