Colon cancer patients who are overweight or obese when diagnosed appear to face a slightly higher risk for developing a second weight-related cancer, new research suggests.
The finding didn’t speak to the risk of colon cancer recurrence, only the potential for developing other cancers associated with obesity.
“We found that colorectal cancer survivors who reported being overweight or obese prior to diagnosis had a modestly increased risk of developing an obesity-related second cancer compared to [cancer survivors] who reported a normal weight,” said study lead author Todd Gibson, who conducted his research while a fellow with the U.S. National Cancer Institute.
A higher obesity-driven risk was identified for kidney, pancreatic, esophageal and endometrial cancers, as well as for postmenopausal breast cancer among female colorectal cancer patients.
Gibson, now an assistant faculty member at St. Jude Children’s Research Hospital in Memphis, and his colleagues discussed the findings in the Sept. 29 online edition of the Journal of Clinical Oncology.
The authors noted that roughly 1.1 million Americans are living with colon cancer, and obesity has long been cited as a contributing risk factor for the disease.
However, in most cases colorectal cancer has a relatively high survival rate, with roughly 70 to 90 percent of patients living to the five-year mark following their diagnosis.
To assess how obesity might affect additional cancer risk post-survival, the research team focused on nearly 12,000 colon cancer survivors who were about age 69 on average when first diagnosed.
Patient weight had been assessed prior to their initial diagnosis by means of a body mass index calculation. BMI readings are based on height and weight.
In all, 44 percent of the patients were deemed overweight (a BMI between 25 and 29), while one-quarter were obese (a BMI of 30 or more).
When compared with colorectal cancer survivors who had been at “normal” weight at diagnosis, those who had been overweight or obese faced a greater risk for developing a second obesity-related cancer down the road.
However, the team stressed that the actual risk that an obese or overweight colon cancer survivor would develop a secondary cancer remained low, even if their relative risk was almost double that of normal-weight survivors.
Also, the risk for developing one of the obesity-related cancers was actually no higher among obese and overweight colon cancer survivors than it was for obese and overweight members of the general public who’d never had colon cancer.
In other words, the smoking gun appears to be obesity itself, rather than a prior history of cancer.
“The implication,” said Gibson, “is that maintaining a healthy weight is important for cancer prevention in colorectal cancer survivors, just as it is in the general population. [So] our results further emphasize the importance of existing guidelines recommending healthy weight for survivors.”
Dr. Andrew Chan, an associate professor in the department of medicine at Harvard Medical School in Boston, said the study “not only supports the importance of considering obesity as a risk factor for colorectal cancer, but also suggests that it remains a predictor of survival after one has been diagnosed.”
The finding has “important implications as the average risk of developing colorectal cancer over one’s lifetime is estimated to be about 6 percent,” Chan said. “Thus, for this large number of individuals, working to maintain an ideal body weight remains a high priority.”
Dr. David Carr-Locke, chief of the division of digestive diseases at Mount Sinai Beth Israel Medical Center in New York City, seconded the thought.”The message is obviously that here we have yet another reason why it’s better not to be obese,” he said. “Of course, we certainly don’t know all the answers about how cancer risk works. What part is genetic? What part is environment? But it does look like obesity itself does have an influence on the risk for some cancers.”