Bariatric surgery appears to decrease the risk for some cancers, but it may increase the risk for others, particularly colorectal cancer (CRC), according to a synthesis of current evidence.
“There has been a recent burst of studies examining the association between bariatric surgery and the longitudinal risks of developing cancer,” corresponding author Zhi Ven Fong, MD, MPH, DrPH, surgical oncologist, Mayo Clinic Arizona, Phoenix, said in an interview. “However, there has not been a rigorous and critical analysis of the data published to date.”
In evaluating research showing an association between bariatric surgery and longitudinal cancer risk, the investigators found that the quality of the studies and their findings are “heterogeneous and might be susceptible to bias,” Dr. Fong said.
Bariatric surgery appears to have the strongest and most consistent association with the reduction of breast, ovarian, and endometrial cancer risk, first author Pei-Wen Lim, MD, MS, bariatric surgeon at Mayo Clinic Arizona, Phoenix, told this news organization. “However, there have been concerning signals from preclinical and epidemiological studies that bariatric surgery may be associated with a higher risk of developing colorectal cancers,” she added.
The authors cautioned against certain changes in clinical management.
“First, cancer surveillance frequency should not be altered after bariatric surgery because of any assumed reduction in longitudinal cancer risk, and surveillance strategy should mirror that of an average-risk individual,” they wrote. “Secondly, the indications for bariatric surgery should not be expanded for the purpose of cancer-risk mitigation.”
The review was published online in JAMA Surgery.
Protection Against Hormone-Related Cancers
The authors pointed to several studies that appear to support the association between bariatric surgery and decreased risk for hormone-related cancers.
Among them is an observational study of 6781 patients in Canada that showed a significant reduction in breast cancer risk at a median follow-up of 5 years in those who had bariatric surgery vs those who did not (P = .01).
The largest study to date on risk for hormone-related cancer after bariatric surgery was conducted using New York State data for 302,883 women.
It showed a lower rate of breast, endometrial, and ovarian cancers after bariatric surgery (hazard ratio [HR], 0.78; P < .001), with Roux-en-Y gastric bypass conferring the greatest benefit compared with laparoscopic sleeve gastrectomy (HR, 0.66; P = .006) and laparoscopic adjustable gastric banding (HR, 0.83; P = .006).
Beyond the shared mechanisms explaining obesity and cancer risk, a proposed explanation for the strong, consistent association between bariatric surgery and hormone-sensitive cancers is the role obesity-related changes in estrogen stimulation play in development of such cancers, the authors noted.
Association With GI Cancers
The association between bariatric surgery and development of esophageal, gastric, liver, and pancreas cancers is less clear. The data are heterogeneous, with studies showing either no association or decreased longitudinal incidence, the authors reported.
The data are also mixed when it comes to CRC. Epidemiological studies have demonstrated decreased longitudinal incidence of colon and rectal cancer after bariatric surgery; however, two studies have suggested an increased CRC risk after bariatric surgery, the authors noted.
A 15-year study from England that matched 8794 patients with obesity who underwent bariatric surgery with 8794 patients with obesity who did not have the surgery showed that gastric bypass (but not gastric banding or sleeve gastrectomy) was associated with a greater than twofold increased risk of developing colon and rectal cancer (odds ratio, 2.63).
These findings were corroborated in a Swedish cohort study with more than 10 years of follow-up data.
One potential explanation for the heterogeneous findings is that “present studies do not discriminate the sub-types of colon and rectal cancer, with bariatric surgery possibly increasing the incidence of colitis-associated cancers but not hereditary cancers,” the authors wrote.
“The mechanism by which gastric bypass may increase the risk of colorectal cancer is through changes in the gut’s microbiome. These changes in gut flora may triumph the protective effect of weight loss on the development of colorectal cancers,” Dr. Fong said.
Prospective studies are necessary to better delineate CRC risk after bariatric surgery, the authors wrote.