Bariatric surgery may decrease overall cancer risk in women, but not men, within the first five years after surgery, and according to the study’s researchers the decrease may be explained by a decreased risk of breast and endometrial cancer and non-Hodgkin lymphoma in women.
In the paper, ‘Cancer Risk After Bariatric Surgery in a Cohort Study from the Five Nordic Countries’, published in Obesity Surgery, the authors noted that the risk of obesity-related cancer post-bariatric surgery unknown. Therefore, they designed the study assess the impact of bariatric surgery on cancer risk in a multi-national (Denmark, Finland, Iceland, Norway and Sweden) setting and examined the cancer risk in bariatric surgery patients compared with non-operated patients with obesity.
The study included data from 1 January 1980 to 31 December 2012 and the outcomes were all cancers (excluding non-melanoma skin cancer), obesity-related cancers and specific tumour sites with a minimum of 20 cancer events in the bariatric surgery group. Eight variables that may be associated with both obesity and overall cancer risk were evaluated as potential confounders: age, sex, calendar year, country, length of follow-up, diabetes, chronic obstructive pulmonary disease representing tobacco smoking and alcohol dependency or alcohol-induced diagnoses representing alcohol overconsumption.
In total, the study included 482,572 individuals with obesity, including 49,096 who had undergone bariatric surgery. Compared with non-operated individuals with obesity, bariatric surgery patients had an 11% decreased overall risk of cancer (HR 0.89, 95% CI 0.83–0.94) and the risk was similarly reduced for obesity-related cancer (HR 0.89, 95% CI 0.82–0.97). However, the risk reduction was only found in women (HR 0.86, 95% CI 0.80–0.92), not in men (HR 0.98, 95% CI 0.95–1.01), and the decreased risk was statistically significant only within the first five years of surgery.
Regarding cancer type, an analyses of ten individual cancer sites (with at least 20 cases in the bariatric surgery group) indicated decreased risks of breast cancer (HR 0.81, 95% CI 0.69–0.95), endometrial cancer (HR 0.69, 95% CI 0.56–0.84) and non-Hodgkin lymphoma (HR 0.64, 95% CI 0.42–0.97) in women after bariatric surgery.
Interestingly, the risk of kidney cancer was increased in both sexes following bariatric surgery (HR 1.44, 95% CI 1.13–1.84). The researchers report no statistically significant associations between bariatric surgery and cancer of the colon, rectum, pancreas or thyroid or leukaemia. Although not an obesity-related cancer, HRs were estimated for lung cancer to better understand smoking prevalence. The results showed that lung cancer risk was significantly decreased after bariatric surgery in men (HR = 0.53; 95% CI 0.31–0.89), but not in women (HR = 0.88; 95% CI 0.66–1.18).
The authors reported a decreased cancer risk following bariatric surgery during the initial five years after surgery, and offered that a possible explanation could be that weight loss, which is most substantial during the first post-operative years, has an independent protective effect on cancer. In addition, they note that bariatric surgery patients regain weight with time after surgery, which might limit the protective effect of weight loss on cancer in the longer term. Finally, the authors stated that the type of bariatric procedures performed have changed over time and might contribute to the differential results across follow-up periods; gastric bypass is currently the dominant procedure in the Nordic countries and results in greater weight loss than restrictive procedures that were popular previously. Indeed, previous studies have shown a stronger association between gastric bypass and reduced cancer risk than restrictive procedures.
“In conclusion, this large cohort study of all five Nordic countries indicates that the risk of obesity-related cancer is slightly reduced after bariatric surgery in women, but not in men, and that this reduction seems to attenuate over time after surgery,” the authors concluded. “The decreased risk was particularly strong for breast cancer, endometrial cancer and non-Hodgkin lymphoma in women. A possible increased risk of kidney cancer merits further investigation.”
The study researchers were from the Institutet, Karolinska University Hospital, Stockholm, Sweden, the University of Copenhagen, Copenhagen, Denmark, the Institute for Statistical and Epidemiological Cancer Research, Helsinki and the University of Tampere, Tampere, Finland, the Norwegian University of Science and Technology, Trondheim, Norway, the Icelandic Cancer Society and the University of Iceland, Reykjavik, Iceland, and King’s College London, London, UK.
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