A new study provides more evidence that the substantial weight loss achieved with bariatric surgery offers long-term protection against cancer.
The study found that adults with obesity who had bariatric surgery had a 32% lower risk of developing cancer and a 48% lower risk of dying from cancer, compared with peers who did not have the surgery.
“The magnitude of the benefit was very large and dose-dependent, with more weight loss associated with greater reduction in cancer risk,” lead investigator Ali Aminian, MD, director of the Bariatric & Metabolic Institute, Cleveland Clinic, told this news organization.
The study was published online in the Journal of the American Medical Association.
Best evidence to date
“We know that obesity is strongly linked with different types of cancers, but we didn’t know if losing a significant amount of weight can significantly decrease the risk of cancer,” Dr. Aminian explained.
The SPLENDID study involved 30,318 adults with obesity (median age, 46 years; 77% women; median body mass index, 45 kg/m2).
The 5,053 patients who underwent Roux-en-Y gastric bypass (66%) or sleeve gastrectomy (34%) were matched (1:5) to 25,265 patients who did not undergo bariatric surgery (nonsurgical control group).
At 10 years, patients who had bariatric surgery had lost 27.5 kg (60 pounds) compared with 2.7 kg (6 pounds) for peers who didn’t have the surgery, a difference of 19.2%.
During a median follow-up of 6.1 years, 96 patients in the bariatric surgery group and 780 patients in the nonsurgical control group developed an obesity-associated cancer (incidence rate of 3.0 vs. 4.6 events per 1,000 person-years).
At 10 years, the cumulative incidence of obesity-associated cancer was significantly lower in the bariatric surgery group (2.9% vs. 4.9%; absolute risk difference, 2.0%; 95% confidence interval [CI], 1.2%-2.7%; adjusted hazard ratio [HR], 0.68; 95% CI, 0.53-0.87; P = .002).
Most cancer types were less common in the bariatric surgery group. However, a comprehensive analysis of the impact of bariatric surgery on individual cancer types was not possible.
In the fully-adjusted Cox models, the association between bariatric surgery and individual cancer types was significant only for endometrial cancer (adjusted HR, 0.47; 95% CI, 0.27-0.83).
For the other individual cancers, there was a “trend or signal toward a reduction in their risk after the surgery,” Dr. Aminian said.
He noted that endometrial cancer has the strongest association with obesity, and patients who seek bariatric surgery are typically obese, middle-aged women.
“So, it was not surprising that we had more cases of endometrial cancer than other types of cancer,” he said.
The SPLENDID study also showed a significant reduction in cancer-related mortality at 10 years in patients with vs. without bariatric surgery (0.8% vs. 1.4%; adjusted HR, 0.52; 95% CI, 0.31-0.88; P = .01).
The benefits of bariatric surgery were evident in both women and men, younger and older patients, and Black and White patients, and were similarly observed after both gastric bypass and sleeve gastrectomy.
For the cancer protective effect, patients need to lose at least 20%-25% of their body weight, which is almost impossible with diet alone, Dr. Aminian said.
Obesity is “second only to tobacco” as a preventable cause of cancer in the United States, senior author Steven Nissen, MD, chief academic officer of the Heart, Vascular, and Thoracic Institute at Cleveland Clinic, said in a news release.
“This study provides the best possible evidence on the value of intentional weight loss to reduce cancer risk and mortality,” Dr. Nissen said.