Bariatric surgery reduces risk for certain cancers

Bariatric surgery appeared associated with reduced risk for certain obesity-associated malignancies, according to results of a retrospective cohort study.

Study participants demonstrated reduced risks for endometrial, colon and postmenopausal breast cancers.

"What is surprising is how great the risk of cancer was reduced." Daniel P. Schauer, MD, MSc, associate professor of internal medicine at University of Cincinnati College of Medicine, said in a press release. "[This] study provides an additional reason to consider bariatric surgery."

Schauer and colleagues reviewed medical data from 22,198 patients who underwent bariatric surgery between 2005 and 2012. Follow-up continued through 2014.

Researchers compared individuals who underwent bariatric surgery with 66,427 nonsurgical patients matched for sex, age, BMI and Elixhauser Comorbidity Index. Investigators used multivariable Cox proportional hazards models to assess incident cancers in the two groups.

Shauer and colleagues identified 2,543 incident cancers during mean follow-up of 3.5 years.

Participants who underwent bariatric surgery demonstrated a 33 percent reduced risk for any cancer type.

Risk reductions were greatest for obesity-associated cancers. Specifically, researched resported statistically significantly lower risks for colon cancer, postmenopausal breast cancer, endometrial cancer and pancreatic cancer among those who underwent bariatric surgery.

HemOnc Today spoke with Schauer about the study, the implications of these results, the potential explanations for the findings and the questions that still must be answered in subsequent research.

Question: How did this study come about?

Answer: This study stemmed from the CDC report that indicated up to 44 percent of cancers were related to being overweight or obese. We wanted to find out if losing weight through bariatric surgery would reduce the risk for cancer.

Q: How did you conduct the study?

A: We pooled data from the Kaiser Permanente database on more than 22,000 pateints who underwent bariatric surgery. We carefully matched these patients with more than 66,000 controls. We then followed the cohort for up to 10 years to assess if they developed cancer.

Q: What did you find?

A: Overall, having bariatric surgery reduced cancer risk by one-third. When we specifcally looked at the 13 obesity-related cancers - breast, colorectal, endometrial, gallbladder, gastric cardia, kidney, liver, ovarian, pancreatic and thyroid cancers, esophageal adenocarcinoma, meningioma and multiple myeloma - we found the risk for cancer was reduced more than 40 percent for all patients. Cancers not associated with obesity were reduced by 23 percent with bariaric surgery.

Q: What are the clinical implications of the findings?

A: Having bariatric surgery reduces the risk for cancer, and this can be helpful for patients considering the procedure. There are a lot of other reasons to have bariatric surgery that may be as important, such as reductions in the risk for diabetes and hypertension, as well as improved survival. Our data add to evidence suggesting the benefits of bariatric surgery.

Q: What are the potential explanations of the se findings?

A: There are many reasons why bariatric surgery reduces the risk for cancer. For one, weight loss itself reduces the risk. By losing weight, a lot of changes occur within the body. For example, estrogen increases the risk for postmenopausal breast cancer and endometrial cancer, and the amount of circulating estrogen goes down among women who undergo bariatric surgery. When the amount of estrogen is decreased, the risk for those cancers also decreases. For some of the other cancer types, it may be due to decreased inflamation in the body.

Q: Did any of the findings suprise you?

A: We hoped to see the reduction in the risk for cancer, but we were surprised by the magnitude of the reduction.

Q: Why might the risk for some cancer types be reduced by bariatric surgery but not others?

A: It may be that they are not as strongly associated with obesity, so weight loss will have less of an impact on them. Also, longer follow-up may be necessary to see changes in the risk for these cancers. However, further research is needed to answer these questions.

Q: What questions must be answered in subsequent research?

A: We did not find any reductions in the risk for cancers among men. Part of this is because we did not have a lot of men in our study, so we need a larger study including men to see if weight loss is important for reducing the risk for certain cancers. In addition, we looked only at cancers that occurred after bariatric surgery. It is unknown what happens among patients who have had cancer and then undergo bariatric surgery. Does this surgery decrease their risk for recurrence? We need to look into this with additional research. We also did not look at survival after a cancer diagnosis, so this needs to be explored.

By Jennifer Southall

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