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Examining the Impact of Bariatric Surgery on Mortality in Obesity-related Cancers

5 minute read
Ali Tavakkoli, MD
Ali Tavakkoli, MD

A landmark 2007 paper showed substantial drops in mortality in cardiovascular disease (56%) and type 2 diabetes (92%) following bariatric surgery. But another finding from the study has been largely overlooked: a 60% reduction in cancer mortality.

Why might bariatric surgery and weight loss lead to decreased cancer mortality? Minimally invasive and bariatric surgeon Ali Tavakkoli, MD, chief of the Division of General and Gastrointestinal Surgery at Mass General Brigham, reviewed several hypotheses during a presentation at the American Society for Metabolic and Bariatric Surgery Annual Meeting in June 2025.

The following is a recap of Dr. Tavakkoli's talk.

Exploring links between cancer and obesity

The Cancer Prevention Study II found that 13 cancers are associated with overweight and obesity. The link between each cancer and obesity varies by sex and by the strength of the association. For example, in men, obesity is associated with a fourfold increase in the risk of mortality from liver cancer. In women, there is a lower degree of relevance and connection.

When evaluating the impact of bariatric surgery on cancer outcomes, it is important to keep in mind that the differences in magnitude will vary because the association with obesity will vary.

Dr. Tavakkoli reviewed four theories that could explain why bariatric surgery and weight loss contribute to lower cancer mortality:

  1. Improved screening and early detection
  2. Improved treatment response and outcomes
  3. Altered cancer biology
  4. Reduced cancer incidence

Let's look at each of these proposed mechanisms.

  1. Improved screening and early detection

Multiple studies have demonstrated an association between obesity and lower screening rates. Barriers to screening include stigma, machinery that cannot accommodate patients, inferior imaging quality, and patient discomfort during screening.

Many studies have confirmed that bariatric surgery successfully addresses these issues. For example, the SPLENDID study found much higher screening rates for breast, colorectal, and prostate cancer among patients with obesity who undergo bariatric surgery than those who do not.

Takeaway:

Higher screening rates lead to earlier cancer detection, contributing to reduced cancer mortality.

  1. Improved treatment response and outcomes

A 2024 paper concluded that obesity was associated with poorer outcomes in all 13 cancers outlined in the Cancer Prevention Study II.

Patients with obesity are more likely to have surgical complications like wound infections, which may delay initiation and compromise outcomes of adjuvant therapy. Meanwhile, obesity can complicate chemotherapy and radiotherapy dosing as well as impair treatment efficacy and safety.

Takeaway:

By inducing weight loss, bariatric surgery makes cancer treatment more efficacious.

  1. Altered cancer biology

Dr. Tavakkoli was a co-author of a retrospective cohort study examining the association of bariatric surgery status with HER2+ breast cancer, a typically aggressive subtype. The study looked at 42 female patients who had developed breast cancer following bariatric surgery (median time between surgery and diagnosis: 48 months).

The investigators concluded that these patients were less likely to develop HER2+ breast cancer than a cohort of 84 nonsurgical controls matched based on body mass index at the time of diagnosis. While underpowered to reach statistical significance, the study also suggested improved survival trends in the bariatric surgery patients.

Takeaway:

For reasons that are not yet understood, bariatric surgery can change the biology of cancer — even if cancer develops later.

  1. Reduced cancer incidence

The SPLENDID study compared 5,053 bariatric patients with 25,265 matched nonsurgical controls over a median follow-up of 6.1 years. Cancer incidence was 2.9% in the surgical group versus 4.9% in the control cohort. Interestingly, cancer reduction was nearly identical across Roux-en-Y gastric bypass (n=3,348) and sleeve gastrectomy (n=1,705). In addition, greater weight loss was found to be correlated with a greater decline in cancer incidence.

Why might bariatric surgery lead to a decrease in cancer incidence? Possible mechanisms at play include:

  • Resolution of chronic inflammation
  • Favorable shifts in levels of insulin, adipokines, and steroid hormones
  • Dietary changes
  • Changes in the microbiome
  • Improved immunosurveillance

Dr. Tavakkoli was a co-author of a 2018 paper exploring immunosurveillance — in particular, the role of white blood cells called natural killer (NK) cells. In healthy individuals, NK cells recognize and destroy cancerous or precancerous cells. But in patients with obesity, fat accumulation in NK cells results in metabolic paralysis, eliminating their ability to kill abnormal cells.

The investigators determined that by removing fat from NK cells, NK immunosurveillance activity is restored, which may in turn lead to lowered cancer incidence.

Takeaway:

Reduced cancer incidence is driven through several likely mechanisms, including immunosurveillance.

What comes next?

Dr. Tavakkoli asserts that when counseling patients on weight-management options, such as GLP-1 based drugs, physicians often overlook the beneficial impact of bariatric surgery on cancer incidence and mortality. Studies comparing the impact of different weight-loss strategies on cancer mortality and incidence remain an area of investigation.