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  • Bariatric surgery is an extremely effective tool for obesity.
  • The procedure’s effects on various forms of cancer is not well understood.
  • A new review now sheds some light on the relationship between bariatric surgery and cancer.

Bariatric surgery appears to decrease the risk of certain forms of cancer, but may increase the risk of others, according to a new scientific review. The authors say their findings underscore the need for more research on the issue before making confirmatory statements about the effects of the procedure on cancer risk.

In the fight against the obesity epidemic, bariatric surgery is one of the most effective, evidence-based treatments available. The procedure is known to improve outcomes related to numerous other health problems, including heart disease, type 2 diabetes, and high blood pressure.

Treating obesity is commonly viewed as an “upstream” way of preventing other more serious conditions later on. Since bariatric surgery is so effective for obesity, it might stand to reason that it could be effective at helping to prevent the many forms of cancer associated with obesity.

But the truth is more complicated.

Bariatric surgery’s association with increased cancer risk is not well established. In a review published today in JAMA Surgery, researchers found differing results for how the procedure affects different forms of cancer.

“Our review found that the quality of the studies and its findings are heterogenous and might be susceptible to bias,” said Dr. Zhi Ven Fong, a Surgical Oncologist at Mayo Clinic Arizona and author of the review told Healthline.

“The data where there has been good consistency is the reduction of breast, ovarian, and endometrial cancer risk with bariatric surgery. 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,” he added.

However, it is important to note that the review doesn’t prove a causal link between bariatric surgery and cancer risk. Nor does it cast doubt on the overall effectiveness of bariatric surgery.

“This review makes the point that there are consistent positive associations and negative associations for certain types of cancer as they relate to bariatric surgery, and then there is a gray zone where there are conflicting results from different studies,” said Dr. Cindy Kin, an Associate Professor of Surgery at Stanford Medicine who was not involved in the research, told Healthline.

Researchers found that bariatric surgery had the greatest association with lowering the risk for cancers associated with hormones, including breast cancer, ovarian cancer, and endometrial cancer. In one study of nearly 7,000 patients, those who received bariatric surgery “demonstrated a significant reduction in breast cancer risk” at an average 5-year follow up period, compared with those who did not.

In what the researchers call “the largest study to date,” of more than 300,000 female patients, individuals who underwent the procedure and lower rates of breast, endometrial, and ovarian cancer.

Scientists believe that the mechanisms for how bariatric surgery affects these cancers has to do with the role of how fat, adipose tissue, affects hormones in the body, like estrogen and insulin. Adipose tissue produces excess estrogen, which is associated with the above-mentioned cancers.

Obese individuals also tend to have more insulin in their bodies, which can also lead to the development of certain cancers.

Leptin, a hormone that is key to metabolism, reproduction, and satiety, is produced in fat cells. However, when it is produced in abundance due to obesity, it too can lead to “aberrant cell proliferation” then cancer.

The relationship between bariatric surgery and other forms of cancer is far less obvious. Historically, esophageal and gastric cancer were believed to be at increased risk due to their physical effects on the digestive tract and the potential to exacerbate acid reflux.

However, the review found that this was not the case: cancer risk was actually similar or slightly improved.

Findings on pancreas and liver cancer were inconsistent.

For colorectal cancer, results were, again, mixed. But the authors note two studies in which colorectal cancer found an increased risk following bariatric surgery.

“Given the potential increased risk of colorectal cancers, caution should be exercised when considering bariatric surgery in patients with increased baseline risk of colorectal cancers such as those with inflammatory bowel disease,” said Fong.

Other experts interviewed by Healthline pushed back on these findings.

“This association of increased incidence of colorectal cancer would not trump all the benefits that are actually causally linked to bariatric surgery. For patients who meet the standard criteria for bariatric surgery, the potential benefits of the surgery outweigh the risks,” said Kin.

Dr. Dan Azagury, section chief of Minimally Invasive and Bariatric Surgery and medical director for the Bariatric and Metabolic Interdisciplinary clinic at Stanford Health was also cautious about the findings.

“We should be very careful about drawing too strong conclusions on the topic of colorectal cancer: as the authors mention, the data is very contradictory,” he said.

Obesity is a comorbidity for many serious health conditions, including diabetes, high blood pressure, and heart disease. It is also associated with an increased risk of 13 different forms of cancer including:

  • Breast
  • Kidney
  • Ovarian
  • Pancreatic
  • Colorectal
  • Liver

Bariatric surgery, sometimes called “weight loss surgery”, modifies the digestive system to reduce the amount of food a patient consumes and helps them feel more full. There are several procedures, such as a gastric sleeve and gastric bypass, that all fall under the name bariatric surgery, but there are others as well.

These procedures are only recommended for those who have class III obesity (a BMI of 40+) or class II obesity (a BMI of 35+) and at least one comorbidity, such as high blood pressure or diabetes.

Bariatric surgery has demonstrated weight loss as much as 77% of body weight. Patients also tend to keep the weight off, averaging 50% of weight loss at five years after the initial operation.

As with any major healthcare decision, patients should discuss the risks and benefits of bariatric surgery with their healthcare provider.

“Healthcare providers should include the potential associations with increased or decreased cancer risk in their discussions with patients as part of the shared decision-making process. Only about 1% of patients who are eligible for bariatric surgery actually undergo the operation, so clearly there is an opportunity here to improve education and counseling for patients with obesity regarding their options,” said Kin.

For many forms of cancer, including liver, pancreas, gastric, and esophageal, the effects of bariatric surgery are unclear, heterogenous, or inconclusive.

There appears to be a strong association between bariatric surgery and decreased risk of hormone-related cancers including breast, endometrial, and ovarian.

Some studies have indicated an increased risk of colorectal cancer after bariatric surgery, however others did not.

Experts agree that for the appropriate candidate, bariatric surgery’s health benefits far outweigh the risks.