Bariatric Surgery (Weight-Loss Surgery) Cuts Obesity-Related Cancer Risk by More Than Half

The association between obesity and certain cancers is now well established. Obesity increases the risk of at least 13 cancers: esophageal, kidney, postmenopausal breast, stomach, colon, rectal, liver, gallbladder, pancreatic, ovarian, uterine and thyroid cancer, and multiple myeloma. Obesity also adversely affects outcomes after a cancer diagnosis.

The cancers most extensively studied in relation to obesity include breast, uterine, colon and prostate cancer (see How does obesity increase cancer risk?).

What Is Bariatric Surgery?

Obesity operations, known as bariatric surgery, involve changes to the digestive system that help with weight loss.

Obesity surgery is performed when diet and exercise programs do not work or when a person has a health problem because of their weight. Some operations limit how much you can eat, while others reduce the body's ability to absorb nutrients; some combine both aims (see our article on types of bariatric surgery ).

Previous studies have found a notable association between bariatric surgery and a reduced incidence of overall cancer and obesity-related cancers.

Who Is Weight-Loss Surgery Recommended For?

Bariatric surgery is a surgical procedure that helps people with obesity lose weight and improve their health. It is a major operation and may not be suitable for everyone.

According to current information, bariatric surgery should be recommended for people who have unsuccessfully tried other weight-loss methods and have a BMI (Body Mass Index) of 40 or higher, or a BMI of 35 or higher with a serious obesity-related health condition, such as heart disease, diabetes or sleep apnea.

What Is BMI?

BMI stands for Body Mass Index and is calculated by dividing a person's body weight in kilograms by the square of their height in meters. It is a measure used to assess body weight in relation to height.

The BMI formula is:

BMI = Weight (kg) / Height (m)²

This formula divides a person's weight by the square of their height. For example, for someone weighing 70 kg and measuring 1.75 m:

BMI = 70 / (1.75)² = 22.86

This value indicates a “normal weight.” BMI values are generally interpreted as follows:

• Below 18.5: Underweight
• 18.5 - 24.9: Normal weight
• 25 - 29.9: Overweight
• 30 or above: Obesity

However, remember that BMI does not measure body fat and may be misleading in muscular individuals.

Halving Cancer Risk

On May 5, 2023, Digestive Disease Week 2023 featured a new study in which researchers found that patients with obesity who underwent bariatric surgery could have more than a 50% reduction in the incidence of obesity-related cancers compared with patients who did not undergo surgery.

In this study, researchers compared data from 55,700 patients with obesity who underwent bariatric surgery and 55,700 patients who did not undergo surgery. The patient group included people who underwent sleeve gastrectomy, gastric bypass or gastric band procedures. The researchers controlled for risk factors that might influence cancer development, including smoking, alcohol use, cardiovascular disease, hormone therapy and other comorbidities.

After 10 years of follow-up, only 4% of patients who underwent bariatric surgery were found to have developed an obesity-related cancer, compared with 8.9% of those who did not undergo surgery.

Patients who underwent bariatric surgery also consistently had fewer new cases of almost all obesity-related cancer types than those who did not undergo surgery. These included breast cancer (501 versus 751), colorectal cancer (201 versus 360), liver cancer (969 versus 2,198), pancreatic cancer (54 versus 86), ovarian cancer (130 versus 214) and thyroid cancer (154 versus 175).

These new findings strongly indicate the potential of bariatric surgery to reduce obesity-related cancer risk and further emphasize its importance in obesity management.

Other Recent Studies on Bariatric Surgery and Cancer Risk

A database study involving more than 16000 patients found the following reductions in patients who underwent bariatric surgery compared with matched nonsurgical patients with obesity:

• 77% in the risk of hormone-related cancers, including breast cancer,
• 79% in uterine cancer risk and
• 63% in prostate cancer risk.

Roux-en-Y gastric bypass (RYGB) produced the greatest reduction in hormone-related cancer risk: 84%. However, it was associated with a 2.6-fold increase in colorectal cancer risk. Adjustable gastric banding and sleeve gastrectomy were not associated with any increase in colorectal cancer risk.

In another multicenter database study, 22 thousand patients who underwent bariatric surgery (61 percent RYGB and 27 percent sleeve gastrectomy) had a 33% lower risk of developing any cancer during an average 3.5-year follow-up than 66 thousand patients who did not undergo bariatric surgery. Surgery was associated with reductions of 42% in postmenopausal breast cancer risk, 50% in uterine cancer risk, 54% in pancreatic cancer risk and 41% in colon cancer risk. Unlike the study above, this study found no reduction in rectal cancer.

A French database study involving more than a million patients showed that people who underwent bariatric surgery (RYGB, sleeve gastrectomy or gastric banding) shared the same colorectal cancer risk as people with obesity who had not undergone bariatric surgery, which was 34% higher than in the general population.

In another multiple-database study involving 28 thousand patients eligible for bariatric surgery, rates of any cancer and of lung, ovarian and uterine cancers after surgery were significantly lower than in nonsurgical controls.

Another retrospective study, including 5053 patients who underwent bariatric surgery and 25265 matched nonsurgical controls, associated bariatric surgery with a 32% lower risk of obesity-related cancer. A 48% reduction in cancer mortality risk was also found.

Studies using the Swedish Obese Subjects (SOS) database showed that bariatric surgery reduced cancer risk from 6 percent to 3.9 percent over 20 years, with a more pronounced effect in women. A study using the Utah Cancer Registry found a 46% reduction in cancer mortality among patients who underwent obesity surgery.

Bariatric surgery is also associated with a 41% reduction in the risk of all skin cancers, including melanoma.

The following table summarizes results from various studies showing how much bariatric surgery reduces cancer risk:

*