Bariatric Surgery Associated With Reduced Risk for Female-specific Cancers

Women who underwent bariatric surgery to combat obesity were less likely to develop any cancer and female-specific cancers, as demonstrated in results published in Gynecologic Oncology.¹

In the Swedish Obese Subjects (SOS) study, which is an ongoing, prospective matched intervention trial comparing bariatric surgery with conventional obesity treatment, bariatric surgery was associated with reduced risk of overall cancer (HR = 0.71; 95% CI, 0.59-0.85; P <.001). The procedure was also associated with a reduced risk for female-specific cancers (HR = 0.68; 95% CI, 0.52-0.88; P = .004).

Researchers said the HR was nearly identical after adjusting for age, BMI and smoking (HR = 0.68; 95% CI, 0.52-0.89; P = .006).

“The association between obesity and cancer is well established and the previously reported protective effect of bariatric surgery on overall cancer in women is confirmed in this report,” wrote the study researchers, led by Åsa Anveden, MD, PhD, Department of Molecular and Clinical medicine, Institute of Medicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.

“The main finding of this study is that bariatric surgery also is associated with reduced risk of female-specific cancer, here defined as breast, endometrial, ovarian, and all other gynecological cancers. The association between bariatric surgery and female-specific cancer is noteworthy as these comprised about half of the observed cancer events in our cohort and are common in the obese population.”

The number needed to treat (NNT) to prevent 1 cancer event over 10 years was 31. The NNT to prevent 1 female-specific cancer event over 10 years was 56.

SOS enrolled 4047 Swedish patients with obesity from September 1987 through January 2001. Among the women in the study who had surgery (n = 1420), 260 (18.3%) underwent nonadjustable or adjustable gastric banding, 970 (68.3%) underwent vertical banded gastroplasty, and 190 (13.4%) had gastric bypass.

Women in the control group (n = 1447) received the conventional treatment for obesity at their primary healthcare center, which ranged from advanced lifestyle advice to basically no professional treatment.

Both groups underwent a baseline examination about 4 weeks before initiation. Researchers then conducted clinical examinations after 6 months and after years 1, 2, 3, 4, 6, 8, 10, 15, and 20. Centralized biochemical examinations were carried out at matching and baseline examinations after years 2, 10, 15, and 20. Participants completed questionnaires at every clinical examination.

There were 267 first-time cancer events in the control group versus 205 in the surgery group. Half of first-time cancers were female-specific, with 135 events in the control group and 97 in the surgery group. Researchers found that the lower incidence of female-specific cancers associated with surgery was closely correlated with baseline serum insulin (P = .022). Patients with medium (HR = 0.62; 95% CI, 0.39-0.97; P = .036) or high (HR = 0.57; 95% CI, 0.38-0.86; P = .007) insulin levels derived greater benefit from surgery. Baseline BMI was not a significant factor (P = .671).

Except for cervical cancer, incidence rates for all female-specific cancer types were lower in the surgery group. However, researchers found that the difference was only significant for endometrial cancer (HR = 0.56; 95% CI, 0.35-0.89; P = .014). Results were similar when women who had undergone hysterectomy and/or oophorectomy were excluded from the analysis.

“The SOS study demonstrates in a prospective fashion what was previously suggested in retrospective studies and meta-analysis—that bariatric surgery is associated with a reduction in the incidence of primary cancer diagnoses, most notably for women and most notably for endometrial cancer,” Peter A. Argenta, MD, associate professor and director of gynecologic oncology at the University of Minnesota’s department of obstetrics, gynecology, and women’s health, wrote in an accompanying editorial.²

“Furthermore, this manuscript is the latest in a series of reports from the SOS study which suggest that bariatric surgery—related weight loss is associated with reduced rates of multiple health hazards, including overall mortality, diabetes, stroke, myocardial infarction, atrial fibrillation, and gout attacks,” added Argenta.

References

1. Anveden Å, Taube M, Peltonen M, et al. Long-term incidence of female-specific cancer after bariatric surgery or usual care in the Swedish Obese Subjects Study. Gynecol Oncol. 2017;145(2):224-229. doi: 10.1016/j.ygyno.2017.02.036.
2. Argenta PA. Attacking obesity-related diseases at the source—Is bariatric surgery the next wave in cancer prevention? Gynecol Oncol. 2017;145(2):219-220. doi:10.1016/j.ygyno.2017.03.511.