Does Bariatric Surgery Increase or Decrease Cancer Risk?
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, Arizona, told Medscape Medical News. “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 “heterogenous and might be susceptible to bias,” 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, Arizona, told Medscape Medical News. “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,” Fong said.
Prospective studies are necessary to better delineate CRC risk after bariatric surgery, the authors wrote.
Benefits Outweigh Risk
“Ultimately, it has been proven that bariatric surgery saves lives by improving the metabolic profile of patients with obesity through reduction in cardiovascular risk factors such as hypertension, diabetes, and nonalcoholic fatty liver disease,” Lim said.
“If patients qualify for bariatric surgery on the basis of their BMI or comorbidities, they should pursue it for its metabolic benefits, but perhaps consider timely or closer-interval screening colonoscopies to monitor for potential colorectal cancer development,” Lim added.
When asked to comment on the review, Marina Kurian, MD, president, American Society for Metabolic and Bariatric Surgery, also pointed to the advantages of bariatric surgery in reducing major adverse cardiovascular events and improving hypertension, hyperlipidemia, and diabetes.
Bariatric surgery reduces many types of cancers, although the data specific to CRC risk with bariatric surgery are mixed, she added.
“The jury is still out,” said Kurian, clinical professor of surgery at NYU Langone Health in New York, who was not involved in the review. “There are papers and meta-analyses that show benefit even in colorectal cancer, but then there are a couple of papers out there that suggest a risk that seems to be specific to men.”
“It could just be a numbers game, where we may not have enough data. We need more granular data that will help address these nuances and really determine what is the actual risk,” Kurian said. “But overall, for cancer, bariatric surgery is a win.”
This research had no specific funding. Fong and Lim had no relevant disclosures. Kurian disclosed relationships with Allergan, Allurion, CineMed, CSATS, Ezisurg Medical, Hernon, Johnson & Johnson, Medtronic, Novo, Stryker, and Vivus.
