Although being overweight with a high body mass index (BMI) is associated with a higher risk for metastatic colorectal cancer (mCRC), patients with stage 4 mCRC who are thin might not fare as well as their counterparts following treatment. This finding is according to results from a study conducted by Duke Medicine.
This prospective observational analysis, the results of which were recently presented at the European Society for Medical Oncology's World Congress on Gastrointestinal Cancer, found that patients with stage 4 mCRC and a low or healthy body weight lived an average of 2.5 months less than patients who were overweight or obese.
The study results surprised researchers, who did not expect patients who were obese to respond as well to treatment due to their increased risks of developing mCRC and cancer recurrence. In fact, evidence suggests that patients who are obese sometimes receive less-than-optimal dosages of cancer drugs because of their weight, or they may have other comorbidities that complicate recovery.
“Contrary to our hypothesis, patients who had the lowest BMI were at risk of the shortest survival,” explains lead author Yousuf Zafar, MD, an associate professor of medicine at Duke.
The study authors examined data pooled from 6,128 treatment-naïve patients with mCRC who were included in 4 different registry studies in the United States and Europe. The average BMI of patients at the start of treatment was 25.3 kg/m2. According to guidelines, the BMI of a healthy adult is between 18.5 and 24 kg/m2, whereas a BMI below 18.5 kg/m2 is considered underweight.
All patients received chemotherapy plus bevacizumab, a drug used for the treatment of metastatic cancer to slow the growth of new blood vessels.
Patients were divided into 4 BMI ranges. Rates of overall survival and progression-free survival were measured (Table 1). Among patients with the lowest BMI (20-24.9 kg/m2), their average survival rate was 21.1 months after starting treatment, whereas patients with the highest BMI (> 35.1 kg/m2) had an average survival rate of 23.7 months.
Although the study found significant differences in how long a patient lived based on BMI ranges, patients of all weights saw similar rates of progression-free survival (an average of 10 months).
However, stresses Zafar, the study results don't indicate that being overweight is protective for patients with cancer undergoing treatment. Rather, a biological mechanism could be at play that might put thinner patients at higher risk of experiencing poor outcomes.
“There may be a relationship between lower BMI and how much treatment patients can tolerate,” Zafar surmises. “I would hypothesize that the lowest weight patients in our analysis received or tolerated less treatment, or received adequate treatment at first, but became too sick to receive additional therapy. That may be where we can focus more attention on improving their outcomes.”
In addition to Zafar, study authors include M. Kozloff, J. Hubbard, E. Van Cutsem, F. Hermann, A.J. Storm, E. Gomez, C. Revil, and A. Grothey. Genentech, Inc., the manufacturer of bevacizumab (Avastin), provided funding assistance for the study.
TABLE 1. Median overall survival for patients with stage 4 colorectal cancer