Colorectal Cancer and Weight Loss Surgery

Severe obesity has been known to be associated with life threatening morbidities including Type 2 diabetes, arthritis, asthma, sleep apnea, hypertension and heart disease.

Epidemiological data have consistently demonstrated that there is an increasing evidence of a positive correlation between increased body weight and malignancies of the breast, pancreas, ovaries, esophagus and the colon. In fact, oncologists even suggest a more aggressive screening for cancers in the obese: especially for breast, uterine, and colorectal cancers.

So, is there an association between colorectal cancer and weight loss surgery?

Researchers believe that dysregulation of energy homeostasis is associated with colorectal carcinogenesis, with insulin resistance (the impaired ability to normalize plasma glucose levels inspite of adequate insulin reserves) being the core of these pathogenesis. The alteration of the patient's hormonal milieu due to weight loss therefore may result in a lower incidence of these cancers.

In a study of 1482 women with severe obesity, it was found that those who had not undergone bariatric surgery had a significantly higher cancer diagnosis rate (5.8 versus 3.6 percent) than did the patients who had undergone bariatric surgery. There is clinical evidence to suggest that obese women who undergo bariatric surgery experience as much as a 42 percent drop in the relative risk for developing a malignancy.

In a retrospective study, researchers compared 1,035 morbidly obese patients who underwent bariatric surgery with 5,746 patients with the same weight profile who did not undergo the operation. They found that the incidence of diagnosis of colorectal cancer in the first group was 70 percent lower than the second group. The study group also reported a significantly lower incidence of other malignancies in the first group.

Given that obesity affects the body in various ways, a single hypothesis cannot fully explain the result of weight loss surgery on the incidence of colorectal cancer. A possible explanation is that excess body fat is responsible for hormonal imbalances which constitute a major risk factor for colorectal malignancies.

The decrease in body weight, as well the increase in the distal small intestine hormone peptide YY (PYY), and glucagon-like peptide 1 (GLP-1), which are secreted by intestinal L cells consequent to weight loss surgery result in an altered metabolic milieu. The chronic low grade inflammation known to be associated with obesity decreases, as does the oxidative stress, resulting in protection from malignancies, including those of the colon.

It is therefore difficult to attribute the decreased risk for cancer to weight loss alone and multiple factors both pre- and post-bariatric surgery have to be evaluated before reaching a conclusion. Another important consideration when considering the impact of weight loss surgery on cancer risk is that diet and exercise have not proven very effective strategies for weight loss in the morbidly obese.

Researchers therefore maintain that even though there are no randomized case control trials to suggest that sustained weight loss through bariatric surgery decreases the risk of death from colorectal cancer, especially in men, who are most at risk for this, weight loss surgery could be protective for colorectal cancer as well as other obesity related malignancies.