Bariatric Surgery Cuts Uterine Cancer Risk by 71 Percent, Researchers Find

TAMPA, Fla. -- Obese women who maintained weight loss after bariatric surgery seemed to have a 71% lower risk of developing uterine cancer as compared with women who were obese and did not undergo surgery, investigators reported here.

Overall, obesity almost tripled the risk of uterine cancer as compared with non-obese women. The cancer risk posed by obesity declined sharply in the subgroup of women who had bariatric surgery and remained significantly lower in patients who kept the weight off versus those who did not (RR 0.29, 95% CI 0.27-0.32).

The retrospective analysis of data does not prove that bariatric surgery reduces the risk of uterine cancer but does add to a growing body of evidence that obesity increases a woman's risk of the cancer, Kristy Ward, MD, said during a presentation at the Society of Gynecologic Oncology meeting.

"A history of bariatric surgery is associated with a substantial and clinically significant reduced risk of uterine cancer," said Ward, of the University of California San Diego. "Our previous work, in agreement with the findings of others, has indicated that the risk of uterine malignancy increases linearly with BMI [body mass index].

"Along with the findings of this current study, this supports that obesity may be a modifiable risk factor related to development of endometrial cancer."

Multiple studies have shown significant associations between obesity and various types of cancer. Among gynecologic malignancies, endometrial cancer has the strongest association with increasing body mass, estimated at about 40% of all endometrial cancers.

Proving that weight loss reduces cancer risk has been difficult, said Ward, as many patients regain weight over time, complicating long-term follow-up needed to study cancer. Observational studies have suggested a reduced risk of breast cancer after intentional weight loss.

Bariatric surgery leads to rapid and substantial weight loss, which tends to be greater and more durable as compared with other methods of weight loss, Ward continued. Good evidence supports resolution of diabetes and cardiovascular risk factors following bariatric surgery. Evidence of a reduced cancer risk is more modest but continues to accumulate.

Ward and colleagues hypothesized that the risk of uterine malignancy would be reduced in women who had a history of bariatric surgery. To test the hypothesis, they reviewed admission records in the nationwide University HealthSystem Consortium database, limiting the search to the time frame of Jan. 1, 2009, to June 1, 2013.

The query produced records for 7,431,858 admissions, including 103,797 patients with a history of bariatric and 44,345 cases of uterine cancer. Investigators separated the patients into currently obese and non-obese groups and further divided them into groups who had a history of bariatric surgery and those who did not.

Overall, non-obese women with a history of bariatric surgery had the lowest risk of uterine cancer at 270/100,000 admissions. Non-obese women without a history of bariatric surgery had the second lowest risk at 496/100,000 admissions.

Among obese patients, those with a history of bariatric surgery had a uterine cancer rate of 682/100,000 admissions, and obese women without a history of bariatric surgery had the highest risk at 1,409/100,000 admissions.

Investigators then calculated the relative risk of uterine cancer as compared with women who were obese and had no history of bariatric procedures. Non-obese women without a history of bariatric surgery had an 81% lower risk (RR 0.19), followed by non-obese women with a history of bariatric surgery (RR 0.29).

Women who were obese despite having undergone bariatric surgery still had 52% lower risk of uterine cancer versus women who were obese and had no history of bariatric procedures (RR 0.48).

Asked to address the potential underlying biologic mechanisms by which bariatric surgery might reduce uterine cancer risk, Ward said the mechanism remains undetermined, but some evidence suggests the surgery reduces inflammation, which is known to play a role in cancer evolution.

In response to another question from the audience, Ward said the investigators did not have the individual patient data needed to evaluate uterine cancer risk by type of bariatric surgery procedure.