Bariatric surgery lowers cancer risk in obese women

NEW YORK (Reuters Health) - New findings from the ongoing prospective Swedish Obese Subjects (SOS) Study show that weight-loss surgery significantly reduces the incidence of cancer in obese women.

Although cancer incidence was not an end point of the study, the SOS researchers observed that cancer was the most common cause of death, leading them to investigate the effect of bariatric surgery on cancer incidence.

According to the report in the June 24 online issue of The Lancet Oncology by Dr. Lars Sj�str�m from The Sahlgrenska Academy in Gothenburg, Sweden and associates, study participants were between the ages of 37 to 60 years. The minimum BMI was 34 kg/m� for men and 38 kg/m� for women, corresponding to a doubled mortality as compared with a normal BMI.

Between 1987 and 2001, the study enrolled 1420 women and 590 men who underwent bariatric surgery and a roughly equal number of matched controls who received usual care. All patients were eligible for bariatric surgery; the decision to undergo the procedure was based on patient choice. The median follow-up period was 10.9 years.

Cancer incidence was significantly reduced in women who had the surgery (hazard ratio 0.58, p = 0.001), but not in men (HR 0.97, p = 0.90).

Dr. Sj�str�m and his co-investigators observed no associations between cancer incidence and weight loss or reduced energy intake. Thus, they conclude, "the intriguing but unproven possibility that the beneficial effects of bariatric surgery on cancer are mediated by mechanisms other than weight loss or reduced energy intake needs to be further explored."

In a linked commentary, Dr. Andrew G. Renehan from the University of Manchester, UK, remarks that the absence of effect in men may simply reflect the fact that fewer than one third of the subjects were male.

Another possibility he suggests is that in women, "the greatest cancer-prevention effects from weight reduction are likely to be for post-menopausal breast and endometrial cancers..., the effects of which might manifest within a decade." By contrast, "the effects of weight reversal might take much longer to become apparent for other obesity-related cancers, such as colon, rectal, and kidney cancers, which are numerically more common in men."

Nevertheless, Dr. Renehan concludes, "The establishment that the development of (obesity-related) cancers is reversible brings about an encouraging new paradigm in cancer prevention."

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