Bariatric Surgery Reduces Cancer Incidence in Women
Bariatric Surgery Reduces Cancer Incidence in Women
Abstract & Commentary
By William B. Ershler, MD
Synopsis: In a prospective analysis of weight-reduction surgery, the long-term cumulative risk of both non-fatal and fatal cancer was significantly reduced in women, but not in men.
Source: Sjostrom L, et al for the Swedish Obese Subjects Study. Lancet Oncol. 2009;10:653-662.
It is now well established that obesity is a risk factor for cancer. In a recent meta-analysis including 282,000 incident cancer cases and over 133 million person-years of follow-up, a high body-mass index (BMI) was associated with an increased incidence of many types of cancer.1 Yet, it remains to be established whether intentional weight loss would protect against malignancy. Evidence in this regard was recently reported from two retrospective studies of bariatric surgery for obesity,2,3 both of which showed reductions in overall cancer incidence in patients who underwent surgery compared with those who did not.
The current report is an analysis of the Swedish Obese Subjects (SOS) study, which is a prospective, controlled, interventional trial that examined the effect of long-term weight loss on disease and death rates. In fact, results from this study, with regard to reduced mortality in surgically-treated patients, have already been reported.4 The aim of this analysis was to determine whether bariatric surgery was associated with reduced overall incidence of fatal and non-fatal cancer.
The SOS study started in 1987, and involved 2,010 obese patients (body-mass index [BMI] ≥ 34 kg/m2 in men, and ≥ 38 kg/m2 in women) who underwent bariatric surgery and 2,037 contemporaneously matched obese controls who received conventional treatment. While the main endpoint of SOS was overall mortality, the main outcome of this exploratory report was cancer incidence until Dec 31, 2005. Cancer follow-up rate was 99.9%, and the median follow-up time was 10.9 years (range 0-18.1 years).
In the surgery group, 376 patients underwent nonadjustable or adjustable banding, 1,369 underwent vertical banded gastroplasty, and 265 underwent gastric bypass. Omentectomy was not done in any of the operated cases. Control participants received the customary treatment for obesity at their centers of registration. The quality of treatment ranged from advanced lifestyle advice at some sites to no treatment at all in many practices. The treatment of controls started at baseline, varied in duration, and was interrupted and restarted in many cases. Cancer incidence was obtained by cross-checking social security numbers from the SOS database with the Swedish National Cancer Registry, the Cause of Death Registry, and the Registry of the Total Population.
Bariatric surgery resulted in a sustained mean weight reduction of 19.9 kg (SD 15.6 kg) over 10 years, whereas the mean weight change in controls was a gain of 1.3 kg (SD 13.7 kg). The number of first-time cancers after inclusion was lower in the surgery group (n = 117) than in the control group (n = 169; HR 0.67, 95% CI 0.53-0.85, p = 0.0009); the sex-treatment interaction p value was 0.054. In women, the number of first-time cancers after inclusion was lower in the surgery group (n = 79) than in the control group (n = 130; HR 0.58, 0.44-0.77; p = 0.0001), whereas there was no effect of surgery in men (38 in the surgery group vs. 39 in the control group; HR 0.97, 0.62-1.52; p = 0.90). Similar results were obtained after exclusion of all cancer cases during the first three years of the intervention.
Commentary
Thus, bariatric surgery was associated with reduced cancer incidence in obese women but not in obese men. Previous data had supported obesity as a risk factor, but demonstrating that intentional weight loss is protective has been difficult to come by. Dietary interventions for obesity have been disappointing, with low long-term success rates. Bariatric surgery, however, has proven more successful in achieving long-term weight control, and now there are sufficient numbers that retrospective analyses, such as those recently reported,2,3 have provided hints of the potential for cancer prevention by such an approach. The current report strengthens this argument by providing data from a prospective cohort.
Of course, the study is not perfect, nor is it likely to be done in a manner that would satisfy a clinical trial perfectionist. Although well-matched, it was not a randomized study and, conceivably, factors that motivate one to select surgery might also play a role in cancer prevention. Yet, with the data available to date on the benefits of bariatric surgery, including reduced heart disease, diabetes, and overall mortality, to perform a randomized trial of bariatric surgery in morbidly obese patients might be considered ethically inappropriate, let alone hugely expensive.
In a way, this is unfortunate because there are several questions yet to be resolved. These include the curious observation that the salutary effect was demonstrated in women only. It is possible that this may relate to a lower relative weight at the time of intervention in the males, or to the observed smaller effect of surgery on men. However, a similar finding was also reported in one of the retrospective reports.2 Another of the questions is whether the effect is only on obesity-related cancers, as has been suggested.2 Although the current study was insufficiently powered to answer this question, it appeared that the reduction in overall cancer in the female surgery group emanated from a variety of cancer types, indicating a more broad effect than just a reduction in obesity-related tumor incidence.
References
1. Renehan AG, et al. Body-mass index and incidence of cancer: A systematic review and meta-analysis of prospective observational studies. Lancet. 2008; 371:569-578.
2. Adams TD, et al. Cancer incidence and mortality after gastric bypass surgery. Obesity (Silver Spring). 2009; 17:796-802.
3. Christou NV, et al. Bariatric surgery reduces cancer risk in morbidly obese patients. Surg Obes Relat Dis. 2008;4:691-695.
4. Sjostrom L, et al. Effects of bariatric surgery on mortality in Swedish obese subjects. N Engl J Med. 2007; 357:741-752.
In a prospective analysis of weight-reduction surgery, the long-term cumulative risk of both non-fatal and fatal cancer was significantly reduced in women, but not in men.Subscribe Now for Access
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