MBS patients have a greater risk for multiple cancer types compared with the general population

All-cancer incidence risk is similar between patients who underwent metabolic and bariatric surgery (MBS) and the general population, according to a study led by researchers from Örebro University, Örebro, Sweden. They reported that although breast and skin cancer risks were lower among MBS patients compared with controls, MBS patients still had a greater risk for multiple cancer types compared with the general population.

As a result, they concluded that patients who have undergone MBS should continue to undergo the same cancer screening and clinically approved work-up for cancer symptoms, as is recommended for the general population.

Although previous studies have found that MBS reduces the overall risk for cancer compared with non-surgically treated patients with severe obesity, it remains unclear how the risk confers to a general population who has not undergone MBS. Therefore, the researcher sought to evaluate the risks for incident cancer after MBS compared with the general population.

Through the Scandinavian Obesity Surgery Registry, all adults who underwent a primary Roux-en-Y gastric bypass (RYGB) or sleeve gastrectomy (SG) for obesity from January  2007 to December 2020, were identified. The surgical group was matched 1:10 to controls from the general population using exact matching based on age, sex, and area of residence. The current obesity prevalence in the control group is estimated to be equal to that of the general population, approximately 16%.

Cases and controls for whom the case had a previous cancer diagnosis or a diagnosed cancer within the first year after surgery were excluded. Controls with previous cancer or a diagnosed cancer within the first year after index date were also excluded. The main outcome measure was risk of developing cancer after the index date.

Outcomes

The researchers identified 73,092 patients who underwent a primary RYGB or SG from 2007 until 2020 and 730,920 matched controls. After exclusion of 4,668 patients with previous cancer in the surgical group (6.4% cancer prevalence) and their matched controls. They further excluded 43,296 patients in the control group with prevalent cancer (5.9%) but did not exclude their matched MBS patients. Following these extractions, 68,424 patients remained in the surgical group with 640,944 matched controls with varied matching ratio between 1:1 and 1:10.

Mean (SD) follow-up time in the surgical group was 7.7 (3.39) years and 7.8 (3.39) years in the control group. In the surgery group, 55,358 patients underwent RYGB, and 13,066 patients underwent SG. Compared with patients undergoing SG, patients undergoing RYGB were of similar age 40.5 [11.1] vs. 40.6 [10.80] years), had higher BMI values (42.3 [5.46] vs. 39.8 [5.81] kg/m2; Tables S2–S3), and were followed for a longer period (8.5 [3.17] vs. 4.5 [2.09] years). BMI loss at 2 years after surgery was 13.8 (4.32) kg/m2 after RYGB and (10.7) (4.36) kg/m2 after SG, corresponding to a total weight loss of 32.4% (8.41%) and 26.7% (9.32%), respectively.

During follow-up, 3,326 patients in the surgery group and 30,497 matched controls were diagnosed with cancer, with no difference between the groups (IRR: 1.03, 95% CI: 0.99–1.07, p=0.129; Figure 1). Lower IRR was seen in the surgery group for breast cancer in women and melanoma, as well as nonmelanoma skin cancer. A higher risk compared with the general population remained for colon cancer, liver cancer, pancreatic cancer, corpus uteri cancer, renal cancer, malignant meningioma and non-Hodgkin's lymphoma.

Figure 1: Kaplan–Meier estimates for overall cancer-free survival comparing patients who underwent metabolic and bariatric surgery with a matched control group from the general population.

The risk for renal cancer remained increased after both RYGB and SG. An increased risk for colon cancer, liver cancer, and pancreatic cancer was seen after RYGB but not after SG. Although similar trends were seen for malignant meningioma and non-Hodgkin's lymphoma (increased risk) and malignant melanoma (reduced risk), a significant association was only observed after RYGB. A reduced risk for breast cancer among women was seen after RYGB but not after SG. Further post hoc comparison of RYGB and SG showed lower association with pancreatic cancer after SG (HR: 0.13, 95% CI: 0.02–0.96, p=0.046) but higher risk for breast cancer among women (HR: 1.38, 95% CI: 1.03–1.84, p=0.030) and higher risk for nonmelanoma skin cancer (HR: 2.07, 95% CI: 1.29–3.59).

Of the 13 cancer types deemed to be associated with obesity, endometrial, ovarian, hepatocellular, colon, pancreatic, kidney (renal cell), and thyroid cancer and meningioma remained elevated after MBS. compared with the general population. Of the cancer types with a weaker association with obesity, non-Hodgkin's lymphoma remained elevated after MBS. The rates of breast cancer and skin cancer were the only obesity-related cancer types found to have a lower incidence after MBS compared with the general population.

The researchers added that the reason for differences between RYGB and SG is not clear.

The findings were reported in the paper, ‘Risk for cancer after bariatric surgery compared with the general population: a nationwide matched cohort study’, published in the journal Obesity. To access this paper, please click here