In a new study, researchers found obese people who had bariatric or weight-loss surgery and lost more than 20% of their total weight were 50% less likely to develop cancer compared to patients who did not have as much weight loss after surgery.
The research was conducted by a team at Oregon Health & Science University School of Medicine in Portland
The team reviewed data from 2,107 adults who underwent bariatric surgery, either laparoscopic gastric bypass or gastric banding.
The average age of patients was 46 years old, 79% were female, about a third had type 2 diabetes and 44% had a history of smoking before surgery.
Weight and cancer serum biomarkers (proteins detected in the blood, urine or body tissues) were measured before and one year after surgery.
Previous studies have shown that bariatric surgery reduces the risk of certain cancers compared to patients who do not have the surgery.
This study compared the differences in risk based on the amount of weight loss after bariatric surgery.
The team found having a body mass index (BMI) of 30 or more one year after bariatric surgery was suggestive of a 60% higher risk of cancer compared to having a BMI under 30.
About 6.2% of those that lost less than 20% of their body weight reported a cancer diagnosis by year 7, compared to about 3.6% of patients who lost 20% or more of their total body weight—representing a 50% reduction.
Overall, the average BMI at 12-months after surgery was 33 and the average excess weight loss was 58%.
The most common cancer type was breast cancer (34%), followed by thyroid (8.5%), melanoma (7%), colon (6%), kidney (6%), uterine (5%), and lung (4%).
The incidence of bladder, cervical, prostate, brain, endometrial, esophagus, stomach, and testicular was less than 3%.
The study suggests that there is a weight loss threshold, that if achieved, significantly reduces the risk of cancer in post-bariatric surgery patients.
The researchers also found that metabolic changes after bariatric surgery contributed to lowering the risk of cancer.
For each 20% reduction in leptin, a hormone released from the fat cells located in adipose tissue, there was a 20% reduction in cancer incidence.
Decreases in diabetes-related fasting glucose, proinsulin, insulin, and C-peptide levels and increased levels of ghrelin, the hunger hormone, were also associated with reduced cancer risk.
According to the American Society of Clinical Oncology (ASCO), obesity is a major unrecognized risk factor for cancer.
There is increasing evidence linking it to several cancers including those of the breast, prostate, and colon.
Obesity has also been associated with an increased risk of recurrence and mortality in patients with cancer.
The lead author of the study is Andrea M. Stroud, MD, MS, Assistant Professor of Surgery.
The study is published in the Morbidity and Mortality Weekly Report.
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