Bariatric surgery (BS) is becoming an increasingly popular option for patients with obesity and include the vertical sleeve gastrectomy, Roux-en-Y gastric bypass, and laparoscopic banding. Adequately treating obesity is crucial to a patient’s overall health, especially considering the potential risk for cancer, given that obesity can increase an individual’s propensity for certain gastric, gastroesophageal, and gastrointestinal cancers, and can even  promote these malignancies’ progression.1 In addition to its established impact on comorbidities associated with obesity, including hypertension and diabetes, there is great research interest in how BS may alter a patient’s risk for colorectal cancer (CRC), specifically.

The development of CRC after BS is a somewhat controversial topic, with several studies showing conflicting data. One such recently published retrospective multicenter cohort study conducted in France reviewed more than 1 million patients with obesity.2 A total of 74,131 (7% of the total database reviewed) had undergone BS. BS included laparoscopic banding, vertical sleeve gastrectomy, and gastric bypass.

The mean age of patients undergoing  BS was younger than that of the nonsurgical cohort (57.3 ± 5.5 years vs 63.7 ± 7.0 years), and the overall rate of CRC was found to be 0.6% in the BS cohort compared with 1.3% in the nonsurgical cohort (P <.001). The standardized incidence ratio (SIR) in the nonsurgical cohort was 1.34 (95% CI 1.32-1.36) compared with 1.0 (95% CI, 0.90-1.09) in the surgical cohort. Hazard ratios (HRs) propensity-score–matched for the surgical vs nonsurgical cohort were 0.68 (95% CI 0.60-0.77) for CRC and 0.56 (95% CI 0.53-0.59) for benign colorectal polyps.

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The rates of new CRC diagnoses were lower among patients who had undergone gastric bypass (0.5%) or sleeve gastrectomy (0.5%) than those who had undergone adjustable gastric banding (0.7%; P =.04). The rate of benign colorectal polyps in the nonsurgical cohort was 6.8% compared with 3.5% in the BS group (P <.001). By contrast, compared with gastric bypass and sleeve gastrectomy, higher rates of benign colorectal polyps were seen after adjustable gastric banding (3.1% vs 5.0,%; P < .001).  

The study authors concluded that patients of the same age and body mass index who did not undergo BS had a 34% increased risk for CRC compared with the general population. Patients who had undergone BS had an incident risk that paralleled that of the general population and a 32% lower incident risk for CRC compared with matched nonsurgical patients.

The proposed pathophysiologic mechanisms to explain the decreased risk for CRC in patients who had undergone BS may be linked to changes in the gut microbiome induced by BS, a decrease in harmful comorbidities associated with obesity, increase in physical activity, and decreases in proinflammatory hormones. In interpreting and contextualizing the findings of this study, however, it should be noted that the study only included patients from a French database.

Similar results were found in a United States-based study, in which investigatorsobserved a lower risk for any type of cancer in patients with obesity who sought BS compared with matched control individuals (HR 0.67, 95% CI 0.60-0.74; P < .001).3 This decreased risk also included colon cancer (HR 0.59, 95% CI 0.36-0.97; P =.04).

Not all studies evaluating the risk of CRC in patients who had BS have reported similar outcomes. Tao and colleagues evaluated the incident risk of CRC among patients in Nordic countries (Denmark, Finland, Iceland, Norway, and Sweden).4 The overall SIR of colon cancer increased after BS (SIR 1.56, 95% CI 1.28-1.88), with SIRs increasing 10 or more years after surgery. The overall HR of colon cancer was higher, but not statistically significant in patients undergoing BS compared with nonsurgical patients (HR 1.13, 95% CI 0.92-1.39); however, the HR increased to 1.55 (95% CI 1.04-2.31) 10 to 14 years after BS.

In this study, the authors evaluated colon cancer separately from rectal cancer. The investigators found no increased risk for rectal cancer alone (SIR 1.14, 95% CI0.83-1.52 and HR 1.08, 95% CI 0.79-1.49) and proposed that the type of surgery may impact the underlying mechanism leading to a change in cancer risk, including alterations to the rectal mucosa and exposure to bile acids.

Data from a similar study conducted in England demonstrated an increased risk for CRC in patients who had undergone any type of BS compared with nonsurgical patients (odds ratio [OR], 2.19, 95% CI 1.21-3.96). However, gastric bypass—but not banding or sleeve gastrectomy—was associated with an increased risk for CRC (OR 2.63, 95% CI 1.17-5.95) in this population compared with the nonsurgical population.5

Future studies are needed to clarify the exact risks for CRC development after BS, including research into the pathophysiological mechanisms of all types of BS. The conflicting data that are currently available suggest that the progression to cancer is most likely multifactorial, with a patient’s demographics playing a significant role in cancer presentation. As more research accumulates, whether patients with BS should be screened for CRC more frequently will likely become a more common topic of discussion. In the interim, more aggressive CRC screening and/or surveillance after BS in both symptomatic and asymptomatic patients should be considered.


  1. Berger NA. Young adult cancer: influence of the obesity pandemic. Obesity (Silver Spring). 2018;26(4):641-650. doi:10.1002/oby.22137
  2. Bailly L, Fabre R, Pradier C, Iannelli A. Colorectal cancer risk following bariatric surgery in a nationwide study of French individuals with obesity. JAMA Surg. 2020;155(5):395-402. doi:10.1001/jamasurg.2020.0089
  3. Schauer DP, Feigelson HS, Koebnick C, et al. Bariatric surgery and the risk of cancer in a large multisite cohort. Ann Surg. 2019;269(1):95-101. doi:10.1097/SLA.0000000000002525
  4. Tao W, Artama M, von Euler-Chelpin M,  et al. Colon and rectal cancer risk after bariatric surgery in a multicountry Nordic cohort study. Int J Cancer. 2020;147(3):728-735. doi:10.1002/ijc.32770
  5. Mackenzie H, Markar SR, Askari A, et al. Obesity surgery and risk of cancer. Br J Surg. 2018;105(12):1650-1657. doi:10.1002/bjs.10914