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SOS: No increase in colorectal cancer after bariatric surgery

The latest outcomes from the Swedish Obese Subjects have reported that the risk from colorectal cancer does not rise after bariatric surgery, according to a study by researchers from the University of Gothenburg, Sweden. This finding is important for patients with obesity, and their healthcare professionals, when deciding upon such an operation, the authors noted.

Obesity is a known risk factor for several types of cancer, including colorectal cancer (affecting the colon or rectum). It is already established that bariatric surgery leads to a decrease in overall cancer risk in patients with obesity.

However, some studies on colorectal cancer have shown an elevated cancer risk after bariatric surgery, while others have reported a risk reduction. These conflicting results have raised concerns about this surgery and highlighted the need for more long-term studies analysing the effect of bariatric surgery on colorectal cancer risk, the investigators cautioned.

The study, ‘Long-term incidence of colorectal cancer after bariatric surgery or usual care in the Swedish Obese Subjects study’, published in PLOS ONE, is based on data from the SOS (Swedish Obese Subjects) study, which began in 1987 and is led and coordinated from the Sahlgrenska Academy, University of Gothenburg, as well as data from the Swedish Cancer Register, kept by the National Board of Health and Welfare.

The scientists studied a group of 4,047 individuals with obesity; 2,007 underwent bariatric surgery (surgery group: gastric bypass (n=266), gastric banding (n=376) or vertical banded gastroplasty (n=1,365) and 2,040 individuals received non-surgical obesity treatment (control group). The groups were comparable in terms of sex, age, body composition, risk factors for cardiovascular disease, psychosocial variables, and personality traits.

The median follow-up period of the study exceeded 22 years. Over this time, the surgery group underwent a significant weight loss, while the controls broadly retained their original weight. During the follow-up period, there were 58 cases of colorectal cancer in the surgery group and 67 in the control group with a hazard ratio (HR) of 0.79 (95% CI:0.55–1.12; p=0.183). After adjusting for age, body mass index, alcohol intake, smoking status, and diabetes, the adjusted HR was 0.89 (95% CI:0.62–1.29; p=0.551).

When analysing rectal cancer events separately, there were 19 events in the surgery group and 31 events in the control group - a decreased risk of rectal cancer with surgery was observed (HR = 0.56; 95% CI:0.32–0.99; p=0.045, adjusted HR = 0.61 (95% CI:0.34–1.10; p=0.099), while the risk of colon cancer was unchanged.

Figure 1: Cumulative incidences of colon cancer (A), rectal cancer (B) and CRC (C) after bariatric surgery or usual care in patients of the Swedish Obese Subjects Study


"In this very long-term study, we could not verify that bariatric surgery is associated with changes in colorectal cancer risk in patients with obesity," commented Magdalena Taube, associate professor at the department of Molecular and Clinical Medicine at Sahlgrenska Academy and the lead author of the study. “This result is of high clinical relevance.”

The SOS study is the only prospective, controlled study in the world that examines the very long-term effects of obesity surgery compared with conventional obesity treatment. This very long-term follow-up has been crucial for the conclusion of this study: the risk of colorectal cancer does not increase after bariatric surgery.

"Bariatric surgery leads to a substantial weight loss and better health in most patients, but it's still important to keep up healthy living habits and go for regular check-ups after the operation too," Taube concluded.

Further information

To access this paper please click here


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