Effects of bariatric surgery on cancer incidence in obese patients in Sweden (Swedish Obese Subjects Study): a prospective, controlled intervention trial.
BACKGROUND
Obesity is a risk factor for cancer. Intentional weight loss in the obese might protect against malignancy, but evidence is limited. To our knowledge, the Swedish Obese Subjects (SOS) study is the first intervention trial in the obese population to provide prospective, controlled cancer-incidence data.


METHODS
The SOS study started in 1987 and involved 2010 obese patients (body-mass index [BMI] >or=34 kg/m(2) in men, and >or=38 kg/m(2) in women) who underwent bariatric surgery and 2037 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).


RESULTS
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 3 years of the intervention.


CONCLUSIONS
Bariatric surgery was associated with reduced cancer incidence in obese women but not in obese men.


BACKGROUND
Swedish Research Council, Swedish Foundation for Strategic Research, Swedish Federal Government under the LUA/ALF agreement, Hoffmann La Roche, Cederoths, AstraZeneca, Sanofi-Aventis, Ethicon Endosurgery.
Sjöström
Lars
L
The Institutes of Medicine, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden. lars.v.sjostrom@medfak.gu.se
Gummesson
Anders
A
Sjöström
C David
CD
Narbro
Kristina
K
Peltonen
Markku
M
Wedel
Hans
H
Bengtsson
Calle
C
Bouchard
Claude
C
Carlsson
Björn
B
Dahlgren
Sven
S
Jacobson
Peter
P
Karason
Kristjan
K
Karlsson
Jan
J
Larsson
Bo
B
Lindroos
Anna-Karin
AK
Lönroth
Hans
H
Näslund
Ingmar
I
Olbers
Torsten
T
Stenlöf
Kaj
K
Torgerson
Jarl
J
Carlsson
Lena M S
LM
D000328:Adult; D050110:Bariatric Surgery; D016022:Case-Control Studies; D002149:Energy Intake; D005260:Female; D006801:Humans; D008297:Male; D016555:Matched-Pair Analysis; D008875:Middle Aged; D015999:Multivariate Analysis; D009369:Neoplasms / Q000453:epidemiology* / Q000401:mortality / Q000517:prevention & control*; D009765:Obesity / Q000601:surgery*; D016016:Proportional Hazards Models; D011446:Prospective Studies; D017678:Sex Distribution; D013548:Sweden / Q000453:epidemiology; D015431:Weight Loss