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Bariatric surgery and colorectal cancer

Post-bariatric mortality higher from rectal cancer, not colon cancer

Location and appearance of two example colorectal tumors (Credit: Blausen Medical Communications, Inc)
However, cancer-specific deaths in rectal cancer patients were threefold higher in those who had undergone bariatric surgery, compared to those who had not
The results showed borderline significant association between colorectal cancer-specific mortality and restrictive procedures, and no significant association with gastric bypass or malabsorptive procedures

A study led by researchers in Sweden that patients who has bariatric surgery were more likely to die from rectal cancer, compared to colon cancer. The investigators from Karolinska Institutet, Stockholm, Sweden, said that although this was the first study to examine this issue more research is needed before a definite association can be concluded. If the association is true, they state, clinicians should be made aware of the increased risk and poorer prognosis of rectal cancer in patients with prior obesity surgery. The paper, ‘Colorectal Cancer Prognosis Following Obesity Surgery in a Population-Based Cohort Study’, was published in Obesity Surgery.

Bariatric surgery involves mechanical and physiological changes of the gastrointestinal tract that could promote colorectal cancer progression, therefore the authors hypothesised that this type of surgery is associated with poorer prognosis in patients with colorectal cancer.

To assess their hypothesis, they included all patients with an obesity diagnosis who subsequently developed colorectal cancer in Sweden from 1980 to 2012. The main outcomes were whether they had bariatric surgery and colorectal cancer-specific survival, and the secondary outcome was overall survival, measured through all-cause deaths.

This was a nationwide, population-based cohort study including all patients with a hospital discharge diagnosis of obesity in the Swedish Patient Registry combined with a diagnosis of colorectal cancer in the Swedish Cancer Registry from January 1980 to December 2012.

The outcomes revealed 131 obesity surgery and 1332 non-obesity surgery patients with colorectal cancer. There was a statistically significant increased rate of colorectal cancer deaths following obesity surgery (disease-specific HR 1.50, 95% CI 1.00–2.19). When analysed separately, the mortality rate was more than threefold increased in rectal cancer patients with prior obesity surgery (disease-specific HR 3.70, 95% CI 2.00–6.90), while no increased mortality rate was found in colon cancer patients (disease-specific HR 1.10, 85% CI 0.67–1.70).

The study cohort consisted of 1,463 patients with an obesity diagnosis followed by a colorectal cancer diagnosis during the study period. Among these patients, 1009 had colon cancer (69%), 449 had rectal cancer (31%) and five had both colon and rectal cancer codes.

In total, 131 (9%) had undergone bariatric surgery, while the remaining 1,332 patients had not. A flowchart describing the inclusion and exclusion of patients is presented in Figure 1. The bariatric surgery group was younger and included more women than the non-obesity surgery group, while diabetes and cardiovascular diseases were more common in non-obesity surgery patients.

Figure 1: Disease-specific survival proportion of patients with obesity and colon or rectal cancer in Sweden from 1980 to 2012, according to obesity surgery status

Out of 45 (34%) patients in the bariatric surgery cohort that died during the study period, 32 (24%) died from colorectal cancer. The number of deaths among the non-obesity surgery cohort members was 596 (45%), of whom 354 (27%) died from colorectal cancer. Most patients with colorectal cancer as the cause of death died within the first 5 years of diagnosis.

Colorectal cancer patients who had undergone bariatric surgery experienced higher cancer-specific and overall mortality rates than non-surgical patients. Separate analyses of colon and rectal cancer patients revealed no significant difference in mortality rates between obesity surgery and non-obesity surgery patients with respect to colon cancer.

However, cancer-specific deaths in rectal cancer patients were threefold higher in those who had undergone bariatric surgery, compared to those who had not. Overall survival mirrored the disease-specific survival. In a separate analysis, obesity surgery was categorized according to type of procedure. The results showed borderline significant association between colorectal cancer-specific mortality and restrictive procedures, and no significant association with gastric bypass or malabsorptive procedures.

The researchers also state that they cannot exclude that other confounding factors (eg. changes in lifestyle factors) could have contributed rectal cancer following bariatric surgery, although any such factors should be similar for colon cancer, and they believe that following bariatric surgery lifestyle habits usually change to more healthy behaviours.

The authors acknowledged that this study could not confirm if type of bariatric procedure had an impact on colorectal cancer prognosis as the sample size was not sufficiently powered to evaluate the association between specific types of bariatric procedure and colorectal cancer-specific deaths.

“The overall higher rate of deaths observed in obesity surgery patients in this study contradicts previous findings that obesity surgery is protective of mortality,” the researchers note. “However, our analyses are limited to patients with colorectal cancer, and a majority of these patients succumbed to their cancer (71%). Thus, findings from the all-cause mortality analysis were mainly influenced by disease-specific mortality…we cannot exclude that the findings in the present study are due to chance, in spite of the strong and statistically significant association between obesity surgery and rectal cancer.”

The investigators from Karolinska Institutet were assisted by researchers from Harvard School of Public Health, Boston, US, University of Leeds, St James’s University Hospital, Leeds and King’s College London, London, UK.

This is an open access article distributed under the terms of the Creative Commons Attribution License

To access this paper, please click here

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