Risk for Breast Cancer Reduced After Bariatric Surgery

Bariatric surgery for obesity is associated with a reduced risk of developing breast cancer, new data suggest.

In a matched cohort study of more than 69,000 Canadian women, risk for incident breast cancer at 1 year was 40% higher among women who had not undergone bariatric surgery compared with those who had. The risk remained elevated through 5 years of follow-up.

Dr Aristithes Doumouras

The findings were “definitely a bit surprising,” study author Aristithes G. Doumouras, MD, MPH, assistant professor of surgery at McMaster University in Hamilton, Ontario, told Medscape Medical News. “The patients that underwent bariatric surgery had better cancer outcomes than patients who weighed less than they did, so it showed that there was more at play than just weight loss. This effect was durable [and] shows how powerful the surgery is, and the fact that we haven’t even explored all of its effects.”

The study was published online April 12 in JAMA Surgery.

Protective Association

To determine whether there is a residual risk for breast cancer following bariatric surgery for obesity, the investigators analyzed clinical and administrative data collected between 2010 and 2016 in Ontario. They retrospectively matched women with obesity who underwent bariatric surgery with women without a history of bariatric surgery. Participants were matched by age and breast cancer screening status. Covariates included diabetes status, neighborhood income quintile, and measures of healthcare use. The population included 69,260 women (mean age, 45 years).

Among participants who underwent bariatric surgery for obesity, baseline body mass index (BMI) was >35 for those with related comorbid conditions, and BMI was >40 for those without comorbid conditions. The investigators categorized nonsurgical control patients in accordance with the following four BMI categories: <25, 25–29, 30–34, and ≥35. Each control group, as well as the surgical group, included 13,852 women.

Participants in the surgical group were followed for 5 years after bariatric surgery. Those in the nonsurgical group were followed for 5 years after the index date (that is, the date of BMI measurement).

In the overall population, 659 cases of breast cancer were diagnosed in the overall population (0.95%) during the study period. This total included 103 (0.74%) cancers in the surgical cohort; 128 (0.92%) in the group with BMI <25; 143 (1.03%) among those with BMI 25–29; 150 (1.08%) in the group with BMI 30–34; and 135 (0.97%) among those with BMI ≥35.

Most cancers were of stage I. There were 65 cases among those with BMI <25; 76 for those with BMI of 25–29; 65 for BMI of 30–34; 67 for BMI of ≥35, and 60 for the surgery group.

Most tumors were of medium grade and were estrogen receptor positive, progesterone receptor positive, and ERBB2 negative. No significant differences were observed across the groups for stage, grade, or hormone status.

There was an increased hazard for incident breast cancer in the nonsurgical group compared with the postsurgical group after washout periods of 1 year (hazard ratio [HR], 1.40), 2 years (HR, 1.31), and 5 years (HR, 1.38).

In a comparison of the postsurgical cohort with the nonsurgical cohort with BMI <25, the hazard of incident breast cancer was not significantly different for any of the washout periods, but there was a reduced hazard for incident breast cancer among postsurgical patients than among nonsurgical patients in all high BMI categories (BMI ≥25).

“Taken together, these results demonstrate that the protective association between substantial weight loss via bariatric surgery and breast cancer risk is sustained after 5 years following surgery and that it is associated with a baseline risk similar to that of women with BMI less than 25,” the investigators write.

Nevertheless, Doumouras said, “the interaction between the surgery and individuals is poorly studied, and this level of personalized medicine is simply not there yet. We are working on developing a prospective cohort that has genetic, protein, and microbiome [data] to help answer these questions.”

There are not enough women in subpopulations such as BRCA carriers to study at this point, he added. “This is where more patients and time will really help the research process.”

A Universal Benefit?

“Although these findings are important overall for the general population at risk for breast cancer, we raise an important caveat: the benefit of surgical weight loss may not be universal,” write Justin B. Dimick, MD, MPH, surgical innovation editor for JAMA Surgery, and Melissa L. Pilewskie, MD, both of the University of Michigan in Ann Arbor, in an accompanying commentary.

“In addition to lifestyle factors, several nonmodifiable risk factors, such as a genetic predisposition, strong family history, personal history of a high-risk breast lesion, or history of chest wall radiation, impart significant elevation in risk, and the data remain mixed on the impact of weight loss for individuals in these high-risk cohorts,” they add.

“Further study to elucidate the underlying mechanism associated with obesity, weight loss, and breast cancer risk should help guide strategies for risk reduction that are specific to unique high-risk cohorts, because modifiable risk factors may not portend the same benefit among all groups.”

Dr Stephen Edge

Commenting on the findings for Medscape, Stephen Edge, MD, breast surgeon and vice president for system quality and outcomes at Roswell Park Comprehensive Cancer Center in Buffalo, New York, said, “The importance of this study is that it shows that weight loss in midlife can reduce breast cancer risk back to or even below the risk of similar people who were not obese. This has major implications for counseling women.”

The investigators did not have information on the extent of weight loss with surgery or on which participants maintained the lower weight, Edge noted. “However, overall, most people who have weight reduction surgery have major weight loss.”

At this point, he said, “we can now tell women with obesity that in addition to the many other advantages of weight loss, their risk of getting breast cancer will also be reduced.”

The study was supported by the Ontario Bariatric Registry and ICES, which is funded by an annual grant from the Ontario Ministry of Health and the Ontario Ministry of Long-Term Care. Doumouras, Dimick, Pilewskie, and Edge reported no relevant financial relationships.

JAMA Surg. Published online April 12, 2023. Abstract, Commentary

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