Weight-loss surgery could lower cancer risk in obese women

June 23, 2009

Weight-loss surgery (bariatric surgery) could be associated with reduced cancer risk in obese women, but not in obese men, according to an Article published Online first and in the July edition of The Lancet Oncology.

Obesity and a high body mass index (BMI) are associated with an increased risk of developing many different types of cancer. Indeed, in the US it is estimated that being overweight or obese is responsible for 14% of cancer deaths in men and 20% in women--making this factor the most preventable cause of cancer besides smoking. However, whether treatment to reduce obesity can lower cancer incidence is unclear.

In 2007, The Swedish Obese Subjects (SOS) study--designed to assess the effect of long-term weight loss on disease and death rates--reported that bariatric surgery was associated with reduced overall mortality. Cancer was unexpectedly shown to be the most common cause of death, but the study was not powered sufficiently to assess death due to specific causes.

Therefore, in this study, Lars Sjöström and colleagues used data from the ongoing SOS study to investigate whether bariatric surgery is linked with reduced overall incidence of cancer. The authors also assessed the effects of changed body weight and caloric intake on cancer incidence.

The SOS study compared 2010 obese patients who had weight-loss surgery with 2037 obese patients who received standard treatment (ranging from advanced lifestyle advice to no treatment). Patients aged 37󈞨 years were recruited from 25 surgical departments and 480 primary health-care centres across Sweden between 1987 and 2001. They were followed-up for an average of 10.9 years and assessed at regular intervals to detect cancer.

Findings showed that weight-loss surgery was associated with a substantial reduction in cancer incidence (42%) in obese women, but not in obese men.

Over 10 years, surgery resulted in a sustained average weight reduction of 19.9 kg, whereas conventional treatment led to an average weight increase of 1.3 kg. The number of first-time cancers for both sexes combined was lower in the surgery group (117) than in the standard treatment group (169)--meaning those in the surgery group were 33% less likely to develop cancer. In women, the number of first-time cancers was significantly lower in the surgery group (79) than in the standard treatment group (130)--meaning that women having weight-reduction surgery were 42% less likely to develop cancer. However, surgery had no effect on cancer incidence in men, with 39 cases in the standard treatment group vs 38 cases in the surgery group.

Further analyses showed no association between decreased cancer incidence and weight loss or reduced energy intake. In light of this finding, say the authors, the beneficial effects of weight-loss surgery on cancer might be the result of mechanisms other than weight loss or reduced energy intake, and need to be examined further.

They conclude: "In our study, the significant reduction in overall cancer incidence in the female surgery group emanated from a variety of cancer types, indicating a broad effect of bariatric surgery."

In an accompanying Reflection and Reaction comment, Dr Andrew G Renehan, Department of Surgery, School of Cancer and Imaging Sciences, University of Manchester, UK, says: "The cancer-prevention effects of bariatric surgery seem limited to women, an observation reinforcing the importance of studying mechanisms separately by sex. For the SOS cohort, the absence of effect in men might simply reflect small sample numbers. For women, the greatest cancer-prevention effects from weight reduction are likely to be for post-menopausal breast and endometrial cancers, two hormone-sensitive malignancies, 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."
Professor Lars Sjöström, Sahlgrenska University Hospital, Gothenburg, Sweden. T) +46(0) 70 677 8289 E) lars.v.sjostrom@medfak.gu.se

Dr Andrew G Renehan, Department of Surgery, School of Cancer and Imaging Sciences, University of Manchester, UK. T) +44 (0) 161 4463706 E) arenehan@picr.man.ac.uk

For full Article and Reflection and Reaction, see: http://press.thelancet.com/tloweightloss.pdf


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