Taiwan study links early bariatric surgery to lower breast cancer risk

Taipei, Aug. 13 (CNA) Severely obese women who undergo bariatric surgery early may have a 20 percent lower risk of developing breast cancer than those who do not undergo the weight-loss procedure, according to a study led by physicians at Taipei Tzu Chi Hospital.

The study found that women who underwent sleeve gastrectomy -- which removes about two-thirds of the stomach -- within six months of their first severe obesity diagnosis had a 20 percent lower five-year breast cancer risk than those who did not undergo surgery.

"Previous studies have already shown that bariatric surgery can reduce the incidence of breast cancer, including studies involving Taiwanese populations," Chong Kian-Hwee (張健輝), an attending physician in the hospital's Department of Surgery, told CNA in a phone interview on Wednesday.

"What is different about our study is the timing," Chong, the study's first author, said, explaining that few previous studies have examined whether the timing of bariatric surgery is associated with different breast cancer risks.

To examine the link, Chong and his team used data from TriNetX, a global health research network, drawing on patient records from 19 countries across Europe, the Americas and Asia, and initially identified around 4 million women with a body mass index (BMI) above 35.

A BMI above 35 was considered severe obesity in the study. For a woman who is 160 centimeters tall, that corresponds to a weight of about 90 kilograms.

Patients who underwent sleeve gastrectomy were divided into three groups -- those receiving surgery within six months, six to 12 months, or one to three years after their first recorded severe obesity diagnosis.

Each was compared with a nonsurgical control group matched for factors including age, diabetes and hypertension.

Early vs. delayed surgery

While surgery within six months was associated with a roughly 20 percent reduction in breast cancer risk, no statistically significant reduction was found among those receiving surgery six to 12 months later.

Women who underwent surgery one to three years after their first severe obesity diagnosis had a higher observed breast cancer incidence than women who did not undergo surgery, a finding the research team described as "unexpected."

The researchers said this does not necessarily mean delayed surgery increases cancer risk, as women who delayed surgery may have had more healthcare visits than those who did not undergo the procedure, increasing the likelihood of cancer detection.

Chong noted that patients who undergo surgery within six months may be "more proactive" about their overall health than those who delay treatment, which could partly explain the lower risk seen in the early-surgery group.

That behavioral factor may work alongside biological effects, as long-term obesity can cause metabolic abnormalities and chronic inflammation while raising estrogen and insulin levels, changes that may contribute to breast cancer development, according to Chong.

Implications for Taiwan

Chong said he believed the findings could reasonably be applied to Taiwanese and other Asian populations given the known links between severe obesity, chronic inflammation and metabolic disorders.

The research has also changed his own clinical practice, said Chong, who specializes in both bariatric and general surgery.

For patients with a BMI above 35, Chong said he now raises the benefits, risks and potential complications of bariatric surgery earlier and encourages them to consider the procedure.

"I hope my patients can achieve significant improvement in their weight within a year," Chong said.

Breast cancer is the most commonly diagnosed cancer among women in Taiwan. A total of 3,116 women died from the disease in 2025, making it the second-leading cause of cancer death among women after lung cancer, according to Ministry of Health and Welfare statistics.

Meanwhile, the Health Promotion Administration said in March that 51.3 percent of adults in Taiwan were overweight or obese.

The study was published online in June in The Breast, an international peer-reviewed medical journal.