TAMPA – Women who undergo bariatric surgery to lose weight are about 70% less likely to develop uterine cancer than are obese women who do not undergo such surgery, according to findings from a large retrospective cohort study.
The risk reduction was even greater (81%) among those who maintained their weight loss after surgery. The findings suggest that obesity may be a modifiable risk factor for uterine cancer, reported Dr. Kristy Kay Ward of the Moores Cancer Center at the University of California, San Diego.
Of more than 7.4 million inpatient admissions among women aged 18 years or older who were registered in the University Health System Consortium dataset from Jan. 1, 2009, to June 1, 2013, 103,797 had a history of bariatric surgery, and 44,345 had a diagnosis of uterine malignancy. The overall rate of uterine malignancy was 599/100,000 patients among those without a history of bariatric surgery, and which was 2.8 times higher among obese vs. nonobese patients within this group (1,409 vs. 496 per 100,000).
The overall rate of uterine cancer among those with a history of bariatric surgery was 408/100,000, but the rate was 2.5 times higher among those with persistent obesity after surgery, compared with those who maintained weight loss after surgery (682/100,000 vs. 270/100,000), Dr. Ward said at the annual meeting of the Society of Gynecologic Oncology.
Compared with obese women without a history of bariatric surgery, the relative risk of uterine cancer was 0.29 for women with prior bariatric surgery, 0.19 for women with normal weight after surgery, and 0.48 for women who remained obese after surgery, so the overall risk reduction with surgery was 70%, the maximum risk reduction (for those with normal weight after surgery) was 81%, and the lowest reduction in risk (for those who had surgery but remained obese) was 52%, Dr. Ward said.
Though limited by the retrospective nature of the study and the fact that the data didn’t differentiate between types of bariatric surgery, the findings are notable, because about 50,000 women were diagnosed with uterine cancer in 2013, making it the most common cancer affecting female reproductive organs. Furthermore, endometrial cancer, which accounts for 95% of uterine cancers, is associated with obesity in about 50% of cases, she explained.
In fact, obese women are two- to fourfold more likely to develop endometrial cancer than are women of normal weight, she said.
The current findings suggest that "a history of bariatric surgery is associated with substantial and clinically significantly reduced risk of uterine malignancy," she said, adding: "Our previous work, in agreement with the findings of others, had indicated that the risk of uterine malignancy increases linearly with BMI [body mass index]. Along with the findings of the current study, this supports that obesity may be a modifiable risk factor related to the development of endometrial cancer."
The mechanism for the link between bariatric surgery and reduced uterine cancer risk remains unclear, but fat loss likely plays a role, as adiposity is known to increase endogenous estrogen circulation. The bariatric surgery itself may also "somehow be influencing the immune system and decreasing inflammation," thereby contributing to decreased cancer risk, Dr. Ward noted.
The findings suggest that weight reduction measures, including bariatric surgery in appropriate candidates, are vitally important in obese women, she said.
"Screening of patients, counseling patients about the dangers of obesity, and appropriate referral for bariatric surgery may have great impact on the overall health of this population," she concluded, adding that future research should examine the benefits of bariatric surgery for the reduction of cancer, including endometrial cancer.
Dr. Ward reported having no disclosures.