The risk of colorectal cancer was significantly increased among people who had undergone obesity surgery in a retrospective cohort study of more than 77,000 obese patients enrolled in a Swedish registry.
The increased risk for colorectal cancer was associated with all three bariatric procedures – vertical banded gastroplasty, adjustable gastric banding, and Roux-en-Y gastric bypass – and increased further over time, reported Dr. Maryam Derogar, of the Karolinska Institutet, Stockholm, and her associates. No such pattern over time was seen among the obese patients who did not have weight loss surgery. “Our data suggest that increased colorectal cancer risk may be a long-term consequence of such weight loss surgery,” they concluded.
If the association is confirmed, they added, “it should stimulate research addressing colonoscopic evaluation of the incidence of colorectal adenomatous polyps after weight loss surgery with a view to defining an optimum colonoscopy surveillance strategy for the increasing number of patients who undergo obesity surgery. The study was published online in the Annals of Surgery
To address their “unexpected” finding in an earlier study of an apparent increase in the risk of colorectal cancer after weight loss surgery, but no increase in the risk of other cancers related to obesity, they conducted a retrospective cohort study using national registry data between 1980 and 2009, of 15,095 obese patients who had undergone weight loss surgery and 62,016 patients who had been diagnosed with obesity but did not undergo surgery. They calculated the colorectal cancer risk using the standardized incidence ratio (SIR), the observed number of cases divided by the number of expected cases in that group.
The “substantial increase in colorectal cancer risk, above that associated with excess body weight alone, more than 10 years after weight loss surgery is compatible with the long natural history of colorectal carcinogenesis from normal mucosa to a malignant colorectal cancer,” the authors wrote.
Why the risk was increased is not clear, but one possible explanation could be that the malabsorption effects of the gastric bypass procedure results in local mucosal changes, the authors speculated. Previously, they had identified rectal mucosal hyperproliferation in patients who had undergone obesity surgery, present at least 3 years after the procedure, a finding that was “associated with increased mucosal expression of the protumorigenic cytokine macrophage migration inhibitory factor,” they wrote.
The study’s strengths included the size of the sample, long follow-up, and the validity of Swedish national registry data, while the limitations included the retrospective design and the lack of data on body weight over time.As in the United States and other countries, obesity has been increasing in Sweden, with a corresponding increase in weight loss surgery. Over the last 20 years, the prevalence of obesity in Sweden has doubled, and the annual number of obesity operations performed has increased from 1,500 in 2006 to almost 4,000 in 2009, according to the authors.
After weight loss surgery:
When you wake up after your operation: After a big operation, you wake up in the intensive care unit or a high dependency recovery unit. You usually move back to the ward within a day or so.In intensive care you have one to one nursing care. In the high dependency unit you have very close nursing care. Your surgeon and anaesthetist also keep an eye on your progress.These units are busy and often noisy places that some people find strange and disorientating. You’ll feel drowsy because of the anaesthetic and painkillers.
Eating and drinking:Immediately after weight loss surgery you can’t eat or drink and will take fluids through a drip. When you can drink again, start with sips of water. This is usually within 24 to 48 hours.You’ll gradually build up what you can drink and eat. Most people are able to eat small amounts within a week or so.Some people need a feeding tube to help them maintain their nutrition. It can go into the small bowel or into a vein (a drip). You’re likely to go home with a feeding tube in place. You keep the tube in for 4 to 6 weeks whether or not you’re using it, just in case you have any problems. You’ll see the dietitian most days while you’re in hospital. You can contact them once you get home if you have any problems.