Evidence Mounts for Bariatric Benefit in Obesity-Related Cancer

LAS VEGAS — Two studies that provide further support for a potential benefit of a reduced risk of obesity-related cancers post-bariatric surgery were presented here at Obesity Week 2019.

Camila Ortiz Gomez, MD, reported that a snapshot of data from the National Inpatient Sample (NIS) shows obese patients with no prior bariatric surgery were 21% more likely to have an obesity-related cancer than patients who had undergone bariatric surgery.

And Andrea M. Stroud, MD, from Oregon Health and Science University, Portland, presented data from the Longitudinal Assessment of Bariatric Surgery-2 (LABS-2) study indicating that, after the operation, obese patients need to have lost at least 20% of their body weight — or have a body mass index (BMI) below 30 kg/m² — to have a reduced risk of obesity-related cancer.

"So there seems to be variability in the protective effect of surgery that is dependent on the degree of weight loss," she noted.

The "message should be loud and clear now, that society should be doing more" to reduce the incidence of obesity-related cancers, Michel Gagner, MD, a bariatric surgeon at Sacré-Coeur Hospital in Montreal, Quebec, told Medscape Medical News, here at the session of top papers from the American Society for Metabolic & Bariatric Surgery.

"We're talking about decreasing cancer — stop smoking, do exercise, don't drink," he said. "Well there's another one. We should [make an] impact on weight, especially the upper echelon of weight."

Surgery Reduces Obesity-Related Cancers, Even in Genetically Predisposed

Among other research, a study published in Morbidity and Mortality Weekly Report in 2017 by the Centers for Disease Control and Prevention highlighted that overweight and obesity are associated with an increased risk of at least 13 different types of cancer, Ortiz Gomez, Cleveland Clinic, Weston, Florida, told delegates.

The report also stated that "overweight- and obesity-related cancers accounted for 40% of all cancers diagnosed in 2014," and "about 55% of cancers diagnosed in women and 24% of those diagnosed in men are overweight- and obesity-related cancers."

However, the etiology of this association remains unknown, she stressed.

To specifically investigate the relationship between bariatric surgery and cancer, Ortiz Gomez and colleagues analyzed information from the NIS database on more than 7 million US inpatients during 2010 to 2014.

They identified patients who had been hospitalized for obesity-related cancers: colorectal, liver and biliary tract, pancreas, breast, uterus, ovary, prostate, kidney and urinary, meningioma, and thyroid cancer, and multiple myeloma.

In the multivariable analysis, researchers adjusted for age, gender, ethnicity, hypertension, type 2 diabetes, smoking, genetic predisposition to cancer, and family history of malignancy

There were 1,423,367 obesity-related cancers in patients with a BMI of 35 kg/m² or higher who had no prior bariatric surgery.

And there were 246,668 obesity-related cancers in patients who had undergone bariatric surgery.

Obese patients with no prior bariatric surgery were significantly more likely to have obesity-related cancer than patients who had undergone bariatric surgery (adjusted odds ratio, 1.21; P < .0001).

"Bariatric surgery could significantly decrease the odds of developing cancer in the obese population," Ortiz Gomez observed.

There was also a nonsignificant hint of a lower risk of developing obesity-related cancer in genetically predisposed patients who had undergone bariatric surgery.

That is, among patients who were genetically predisposed to cancer, there were 259 cancers in the patients who were obese and did not have bariatric surgery vs 51 cancers in the patients who had prior bariatric surgery (odds ratio, 1.7; P = .116).

The analysis of this variable did not achieve significance most likely because of the small number of cancers in genetically predisposed patients, senior author Raul J. Rosenthal, MD, director, Bariatric and Metabolic Institute, Cleveland Clinic, Weston, Florida, noted to Medscape Medical News in an email.

"To the best of our knowledge," said Ortiz Gomez, "this is the first study suggesting that bariatric surgery has a protective effect, even in genetically predisposed patients."

The assigned discussant Samer Mattar, MD, professor and chief of the bariatric surgery division, Oregon Health and Science University, Portland, wondered whether the database included information about the different types of bariatric surgery, or about the current weight of patients, but Ortiz Gomez explained that this information was not available.

"We have to be very careful. It's not a longitudinal analysis," Ali Aminian, MD, also of the Cleveland Clinic, commented. "It's a cross-sectional database of hospital admission at the time of discharge...We need a longitudinal study."

"This is not ideal," Ortiz Gomez agreed, "but it can support further studies."

Rosenthal agreed that future research would be helpful to provide a view of cancer development over time, but stresses that the current study provides a useful snapshot of one point in time.

Weight-Loss Threshold for Reducing Cancer Post-Surgery

Meanwhile, Stroud and colleagues aimed to examine how the amount of weight lost and the subsequent changes in serum biomarkers were related to the incidence of cancer among patients who had undergone bariatric surgery.

They identified 2107 patients in the LABS-2 cohort who had undergone bariatric surgery — Roux-en-Y gastric bypass (n = 1552) or gastric banding (n = 555) — at 10 sites in the United States in 2006 to 2009 and who had data at baseline and 12 months, and had 7 years of follow-up.

Patients were a mean age of 46 years and 79% were women. About a third had type 2 diabetes and 44% had a history of smoking.

Participants were divided into tertiles of weight loss: < 20%, 20% to 34.5%, and > 35% of total body weight loss.

On average, patients who had a gastric bypass lost 35% of their body weight, while those who had gastric banding lost 15% of their body weight.

During 8759 person-years of follow-up, 82 patients had a new diagnosis of cancer (936 per 100,000 person-years of follow-up).

Of the 82 cancers, 55 were obesity-related cancers.

Breast cancer was the most common type of cancer: 380 per 100,000 patient-years.

Losing more than 20% total body weight reduced cancer by 30% to 50%.

"Patients that had gastric banding do not seem to have enough weight loss to get a cancer reduction benefit,” Stroud noted.

Post-bariatric-surgery decreases in diabetes-related fasting glucose, proinsulin, insulin, and C-peptide levels, as well as leptin, and increased ghrelin were associated with a reduced risk of cancer.

Study limitations include the fact it was observational with small numbers of cancer and few men.

Nevertheless, "our study suggests that there is a weight-loss threshold, that if achieved, significantly reduces risk of cancer in post-bariatric surgery patients," concluded Stroud.

Obesity Week 2019. Abstract #A108. Presented November 5, 2019.

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