Bariatric surgery reduces not only the incidence of overall cancer in obese women, as has been previously reported, but also the risk for female-specific cancers. In particular, it is associated with a significantly reduced risk for endometrial cancer, new results from the Swedish Obese Subjects (SOS) study indicate.
"Obesity is an important risk factor for cancer [and it] is also associated with more advanced cancer disease and increased cancer mortality," Asa Anveden, MD, University of Gothenburg, Sweden, and multicenter colleagues observe.
"The main finding of this study is that bariatric surgery also is associated with reduced risk of female-specific cancer, here defined as breast, endometrial, ovarian, and all other gynaecological cancers," they add.
Findings were published in the May issue of Gynecologic Oncology.
The SOS study is an ongoing, nonrandomized, prospective controlled trial in which investigators aim to determine the long-term effects of bariatric surgery on multiple health endpoints.
In 2009, SOS investigators reported that bariatric surgery reduced cancer risk in obese women but not in men.
The current analysis involved 1420 women from the SOS cohort who had undergone bariatric surgery and 1447 other women matched as controls who received standard treatment for obesity.
At baseline, the mean age of the cohort was 37 years and the mean body mass index (BMI) was 38 kg/m2 or higher.
Among SOS women, 18.3% had undergone nonadjustable or adjustable gastric banding; 68.3% were treated with vertical banded gastroplasty, and 13.4% underwent gastric bypass.
Controls received standard treatment for obesity at their primary healthcare center.
After their surgery, SOS women lost a mean of 28.0 kg at 2 years, some of which was regained at 10 and 15 years' follow-up, but the weight loss was still significant at approximately 21 kg at both time points.
In contrast, "mean weight changes in the control group were small," Dr Anveden points out.
At a median follow-up of 18.1 years, investigators found that the risk of developing any cancer was 29% lower among women who had undergone bariatric surgery than among controls, at a hazard ratio (HR) of 0.71 (P < .001).
"Of the first time cancers, 49% were female-specific," investigators add.
And among those female-specific cancers, bariatric surgery reduced their incidence by 32% compared with receipt of conventional treatment alone, at an HR of 0.68 (P = .004).
On the other hand, a separate analysis showed that while incidence rates for all types of female-specific cancers except cervical cancer were lower in the surgery group, the difference between the two groups was significant only for endometrial cancer, where surgery reduced the risk by 44% compared with controls (P = .014).
Interestingly, the greater benefit from surgery over conventional treatment in terms of cancer risk reduction was most pronounced in women with medium (P = .36) or high (P = .007) baseline insulin levels relative to those with low insulin levels. As the authors point out, it has been suggested that hyperinsulinemia may be a causal link between obesity and cancer.
In contrast, there was no interaction with baseline BMI. Results were also very similar when adjusted for age, BMI, and smoking.
"The association between bariatric surgery and female-specific cancer is noteworthy as these comprised about half of the observed cancer events in our cohort and are common in the obese population," researchers observe.
Commenting on the SOS study, Peter Argenta, MD, University of Minnesota, Minneapolis, told Medscape Medical News that the SOS findings contain different lessons for physicians.
"Sadly, it is pretty clear now that most current nonsurgical weight-loss strategies do not result in significant, sustained weight loss," Dr Argenta said in an email.
"The SOS study demonstrated — again — that bariatric surgery is effective over a period of at least years and is associated with some health benefits, most notably for women," he added.
However, Dr Argenta cautioned that bariatric surgery carries with it significant" and "evolving" morbidity. For example, patients in the SOS study who underwent bariatric surgery were more likely to seek additional medical care in the early years after bariatric surgery, as he pointed out.
It's also extremely uncertain at what age a drastic medical intervention like bariatric surgery should be undertaken, he noted.
The fact that childhood obesity is a marked risk factor for adult obesity is perhaps reason enough to consider early intervention, reducing later risk for diabetes, cardiovascular disease, and cancer.
On the other hand, "we also have to consider early and late surgical morbidity as well as prolonged metabolic derangement as arguments against early intervention," Dr Argenta observed.
Logically, the decision to offer bariatric surgery to obese women should be tailored to their individual risk for cancer.
"While bariatric surgery appears to reduce the risk of getting cancer, most patients with obesity-related endometrial cancer, for example, will ultimately die of non-cancer-related causes, most notably cardiovascular disease," Dr Argenta said.
"For this reason, bariatric surgery might be most effective in high-risk patients, where it potentially could reduce the risk of developing obesity-related cancer and provide patients with nononcological benefits as well," he added.
Dr Argenta authored an editorial that accompanies the paper, in which he writes: "The SOS study demonstrates in a prospective fashion what was previously suggested in retrospective studies and meta-analysis — that bariatric surgery is associated with a reduction in the incidence of primary cancer diagnoses, most notably for women and most notably for endometrial cancer.
"This manuscript is the latest in a series of reports from the SOS study which suggest that bariatric surgery-related weight loss is associated with reduced rates of multiple health hazards including: overall mortality, diabetes, stroke, myocardial infarction, atrial fibrillation, and gout attacks," he adds.
"Yet despite the benefits that accrued to patients in the bariatric surgery cohort, previous reports from the SOS trial also suggest that patients undergoing bariatric surgery were hospitalized more frequently and used more inpatient and outpatient resources, particularly in the first six years after surgery. Though these costs were partially offset by lower medication cost from years 7-20 following surgery it remains unclear if they were accompanied by improvements in oncologic mortality or quality of life (which was statistically similar between surgically and medically treated patients at 10 years), he notes.
Dr Anveden and Dr Argenta have disclosed no relevant financial relationships.
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