Lower Cancer Risk For Obese Women Who Underwent Weight-Loss Surgery

Editor's Choice
Main Category: Cancer / Oncology
Also Included In: Obesity / Weight Loss / Fitness
Article Date: 24 Jun 2009 - 7:00 PDT

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An article published Online First and in the July edition of The Lancet Oncology indicates that weight-loss surgery known as bariatric surgery could be linked to a reduction in cancer risk in obese women, but not in obese men.

The risk of developing different types of cancer is linked to obesity and a high body mass index (BMI). In fact, in the US, about 14 percent of cancer deaths in men and 20 percent in women are directly related to being overweight or obese; makeing it the most preventable cause of cancer besides smoking. But it is still unknown if treatment to reduce obesity can lower cancer incidence.

A study was designed in 2007 to assess the effect of long-term weight loss on disease and death rates, called The Swedish Obese Subjects (SOS) study. Findings showed that bariatric surgery was linked to reduced overall mortality. The study found that cancer was the most common cause of death, but it was unable to assess death due to specific causes.

Lars Sjöström and his team used data from the ongoing SOS study to look into bariatric surgery and whether it is associated with reduced overall occurrence of cancer. The researchers also evaluated the effects of altered body weight and caloric consumption on cancer incidence.

The SOS study assessed 2,010 obese patients who underwent weight-loss surgery in comparison with 2,037 obese patients who received standard treatment, which varied between advanced lifestyle advices to no treatment at all. Between 1987 and 2001, patients aged 37 to 60 years were recruited from twenty five surgical departments and four hundred and eighty primary health-care centers across Sweden. They were monitored for an average of 10.9 years and regularly assessed to detect cancer.

Results indicated that weight-loss surgery was related to a considerable decrease in cancer occurrence of 42 percent in obese women. This was not the case in obese men.

For over a decade, conventional treatment led to an average weight increase of 1.3 kg, while surgery resulted in a sustained average weight reduction of 19.9 kg. For both sexes combined, the number of first-time cancers was lower in the surgery group than in the standard treatment group (117 cases versus 169 cases). This represents 33 percent less probability in the surgery group to develop cancer. In women, the number of first-time cancers was considerably inferior in the surgery group than in the standard treatment group (79 cases versus 130 cases). This represents 42 percent less probability in the women having weight-reduction surgery to develop cancer. On the other hand, surgery had no effect on cancer occurrence in men, with 39 cases in the standard treatment group versus 38 cases in the surgery group.

Additional research pointed out there was no correlation between fewer cancer occurrences and weight loss or lower energy intake. As a result, the authors say the favorable effects of weight-loss surgery on cancer could be the result of different processes other than weight-loss or decreased energy intake, and need further examination.

They write in conclusion: "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 associated note, Dr Andrew G Renehan, of the Department of Surgery, School of Cancer and Imaging Sciences, University of Manchester, UK, remarks: "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."

"Effects of bariatric surgery on cancer incidence in obese patients in Sweden (Swedish Obese Subjects Study): a prospective, controlled intervention trial"
Lars Sjöström, Anders Gummesson, C David Sjöström, Kristina Narbro, Markku Peltonen, Hans Wedel, Calle Bengtsson, Claude Bouchard, Björn Carlsson, Sven Dahlgren, Peter Jacobson, Kristjan Karason, Jan Karlsson, Bo Larsson, Anna-Karin Lindroos, Hans Lönroth, Ingmar Näslund, Torsten Olbers, Kaj Stenlöf, Jarl Torgerson, Lena M S Carlsson, for the Swedish Obese Subjects Study
DOI:10.1016/10.1016/S1470-2045 (09)70159-7
The Lancet/oncology

Written by Stephanie Brunner (B.A.)
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