ESTES PARK, COLO. — The biggest chunk of the substantial mortality benefit conferred by bariatric surgery comes not from reduced cardiovascular mortality or diabetes-related deaths, but from fewer deaths due to cancer, according to two large studies of more than 20,000 subjects.
The large relative risk reductions in diabetes-related and cardiovascular mortality following bariatric surgery have garnered much attention. But obese individuals have an increased risk of cancer, and the absolute number of cancer deaths avoided following the surgery overshadows deaths due to the other causes, Dr. Daniel Bessesen explained at a conference on internal medicine sponsored by the University of Colorado.
“It has been thought that insulin binding to insulin-like growth factor might promote cancer. People have wondered, if patients lose weight and their insulin levels go down, could this prevent cancer? The data from these two studies suggest so,” observed Dr. Bessesen, professor of medicine at the university and chief of endocrinology at Denver Health Medical Center.
The Swedish Obese Subjects (SOS) study was a prospective, nonrandomized study involving more than 4,000 obese individuals, half of whom underwent gastric bypass surgery by general surgeons in Swedish community hospitals.
The surgery patients had an adjusted 29% decrease in overall mortality at an average 10.9 years follow-up, compared with matched controls. There were 13 fatal MIs in the surgery group, compared with 25 in controls. There were 29 cancer deaths in the surgery arm, compared with 47 in controls (N. Engl. J. Med. 2007;357:741-52).
The other major study was a retrospective cohort study involving 7,925 obese Utah residents who underwent gastric bypass surgery and an equal number of matched controls who did not have the surgery. At 7.1 years of follow-up, the adjusted mortality was 40% lower in the surgery group.
Once again, the biggest absolute benefit was a reduction in cancer deaths. The relative risk of death due to cancer was 60% lower in the surgery group, with a rate of 5.5 deaths per 10,000 person-years, compared with 13.3/10,000 person-years in controls. Deaths due to coronary artery disease fell from 5.9 to 2.6/10,000 person-years, a 56% reduction, while diabetes-related deaths dropped by 92% from 3.4 to 0.4/10,000 person-years (N. Engl. J. Med. 2007; 357:753-61).
Both the Swedish and Utah investigators have recently expanded upon their findings via follow-up studies. The Utah investigators used the Utah Cancer Registry in looking at 6,596 patients who underwent gastric bypass surgery and 9,442 severely obese individuals who did not. During a mean 12.5 years of follow-up, the total incidence of cancer was 34% lower in the surgery group. Cancer mortality was 46% lower (Obesity [Silver Spring] 2009;17:796-802).
The Swedish group reanalyzed the SOS data in terms of the incidence of first-time cancer. They found a 42% decrease during 10 years of follow-up in women who had bariatric surgery, but no significant reduction in men (Lancet Oncol. 2009;10:653-62).
In addition to the reduced risk of death, what other benefits can obese patients realistically expect from bariatric surgery? Dr. Bessesen said gastric bypass—the most popular and effective form of bariatric surgery—consistently achieves roughly a 30% weight reduction, or 50%-60% loss of excess body weight, and this has been maintained at follow-up now stretching out beyond 15 years.
Laparoscopic adjustable gastric band surgery, which is less invasive and less risky, is also less effective, conferring about a 20% weight reduction.
“Laparoscopic band results are variable depending on surgeon expertise. A really good surgeon will get 25% weight loss, an average surgeon more like 16%-18%. Roux-en-Y gastric bypass weight loss results are more consistent,” he said.
Sleep apnea is improved in almost all affected patients after bariatric surgery. So are gastroesophageal reflux, urinary incontinence, and hyperlipidemia. Diabetes is resolved after gastric bypass in 80%-85% of affected patients, and in 60%-70% after laparoscopic adjustable gastric banding. Hypertension is the comorbidity most resistant to resolution; only about half of patients are eventually able to stop their antihypertensive medications after bariatric surgery, Dr. Bessesen continued.
As for the risks of bariatric surgery, with improved surgical techniques the 30-day mortality of gastric bypass has dropped to about 0.5%, with 1%-2% mortality at 2 years. In contrast, the long-term mortality of laparoscopic adjustable gastric banding is only about 0.1%; however, this procedure entails the inconvenience of many follow-up adjustments. Pulmonary embolism, wound dehiscence and infection, anastomotic leaks, and anastomotic stricture are potential complications of bariatric surgery. And about 10% of patients fail to lose substantial weight after bariatric surgery; to date there's no way to identify them in advance.
“It's just a risk you take,” Dr. Bessesen concluded. “This is big-time surgery: big benefits, big risks.”