Research has found that women who undergo bariatric surgery have a lower risk of breast cancer. | Image credit: Visual Generation – stock.adobe.com
According to a prospective clinical trial published in JAMA SurgeryA reduced risk of breast cancer following bariatric surgery in obese female patients was observed primarily in women with hyperinsulinemia.1
Obesity is a major risk factor for breast cancer and as cases continue to rise, a similar increase in breast cancer incidence is expected. In a clinical trial led by the Women's Health Initiative, mortality rates following breast cancer were higher among women who were considered overweight or obese (P < .001) while grade 2 or 3 obesity (body mass index ≥ 35 kg/m2, P < .001).2
Previous studies have found that bariatric surgery is associated with a reduced incidence of cancer in people with obesity.1 The aim of the prospective clinical trial was to explore the association between bariatric surgery and breast cancer in women and to determine whether treatment shows different benefits according to baseline insulin levels.
study design
The study was conducted as a prospective, matched, intervention trial involving Swedish participants who had been diagnosed with obesity. Approximately 25 public surgical departments and 480 primary health care centers in Sweden enrolled eligible participants from September 1, 1987, to January 31, 2001.
Participants in the control group were classified as receiving usual obesity care from their primary healthcare provider and were referred to as the usual care group (n = 1447). The surgery group consisted of 1420 women, of whom 260 underwent non-adjustable or adjustable gastric banding, 970 underwent vertical banded gastroplasty, and 190 underwent gastric bypass.
Result
At baseline, the study population included 2867 women with a mean age of 48 years. The usual care group had more women who were experiencing menopause than the surgery group when measured at baseline (36.6% vs. 30.5%, respectively); P = .001).
The follow-up period averaged 23.9 years, with 66 breast cancer-related events in the surgery group and 88 in the usual care group. The treatment groups showed no significant difference in body mass index in women with and without breast cancer. An unadjusted analysis found that bariatric surgery showed an association with a reduced risk of breast cancer compared with the usual care group. However, this association was no longer relevant after adjusting for age, body mass index, alcohol and smoking habits.
When stratified by menopausal status at baseline, women in the usual care group had a higher incidence of breast cancer. Additionally, premenopausal women had a higher incidence of breast cancer than postmenopausal women.
The benefits of surgical treatment for breast cancer risk were greater in women with baseline insulin levels above the average of 15.8 mlU/L than in women with levels below the average. Only 5 participants were excluded from the study based on incomplete data on baseline insulin.
It was found that the benefit of surgical treatment affected the risk of breast cancer in women with above-average baseline insulin levels compared with women with below-average levels.
While the biological mechanisms by which bariatric surgery reduces breast cancer risk are not fully understood, it has been suggested that weight loss counteracts a potential pathway where obesity can lead to cancer. The results of the Swedish study are consistent with previous data that concluded bariatric surgery to be an associated factor in reducing obesity-induced cancer risk. However, recent reports have shown data on obese women who undergo surgery to have a reduced risk of both premenopausal and postmenopausal breast cancer compared to women who did not undergo surgery.
Limitations of the study included the non-randomized design that resulted in several variables differing between study groups at baseline; the study may have led to sub-optimal matching for some individual variables. In addition, there was no clear distribution of risk factors that favored any group. Each analysis was adjusted for risk factors that were associated with breast cancer. The study also included older surgical methods that are no longer in practice, and information about estrogen levels or breast cancer subtype was not included.
With the advent of new weight loss injection medications such as semaglutide (Wegovy), obesity treatment has become more accessible to eligible patients. Oncology specialists are embracing the belief that weight loss medications can aid in cancer prevention and treatment. Benjamin Liu and Cindy Lin, residents of Case Western Reserve University School of Medicine, told The Guardian“Our findings are significant in that they may change the paradigm for managing obesity by suggesting early intervention with a GLP-1 RA [glucagon-like peptide-1 receptor agonists] The development of obesity-related cancers may be delayed or prevented.”4
The researchers concluded that the study found a reduced risk of breast cancer after bariatric surgery in obese women, particularly those with hyperinsulinemia, indicating that insulin may be a potential predictor of the effect of treatment.
Reference
1. Christensen FM, Andersen-Asarsson JC, Peltonen M, et al. Breast cancer risk after bariatric surgery and the influence of insulin levels: a non-randomized controlled trial. JAMA SurgeonPublished online May 15, 2024. doi:10.1001/jamasurg.2024.1169
2. Santoro C. Metabolic syndrome, obesity contribute to breast cancer mortality in postmenopausal women. AJMCMay 13, 2024. Accessed June 25, 2024. https://www.ajmc.com/view/metabolic-syndrome-obesity-contribute-to-breast-cancer-mortality-in-postmenopausal-women
3. Chlebowski RT, Aragaki AK, Pan K, et al. Breast cancer incidence and mortality from metabolic syndrome and obesity: the Women's Health Initiative. cancer. Published online May 13, 2024. doi:10.1002/cncr.35318
4. Gregory A. “Huge potential”: weight-loss drugs cut cancer risk by a fifth, research suggests. GuardianJune 4, 2024. Accessed June 25, 2024. https://www.theguardian.com/society/article/2024/jun/04/weight-loss-drugs-cut-cancer-risk-fifth-research-wegovy