Multitarget stool DNA testing is as accurate in predicting advanced colorectal neoplasia in patients who have undergone bariatric and metabolic surgery (BMS) as it is in the average-risk population, according to new findings. According to the investigators from Mayo Clinic, the results should reassure clinicians who have been unsure how BMS might affect colorectal cancer detection.

“While there are theoretical concerns that post-BMS anatomy and physiology may alter the performance of mt-sDNA, [and] contribute to false-positive tests and overutilization of follow-up colonoscopy, these concerns were not supported [in our study],” noted the investigators, led by Derek Ebner, MD, a fellow in gastroenterology and hepatology neoplasia at Mayo Clinic in Rochester, Minn. (Gastro Hep Advances 2023;2[7]:902-910).

Patients with obesity are an important target for CRC screening initiatives because they are at a higher risk for CRC, the investigators noted. However, an estimated one-third of eligible patients with obesity are not screened (Am J Prev Med 2017;53[2]:e41-e49).

Administration of noninvasive tests, such as mt-sDNA, may help reduce the rate of unscreened individuals with obesity—as they have been touted to do in the general population. However, the researchers explained there has been a theoretical concern that factors like marginal ulcers related to surgery, postsurgery diarrhea from dumping, bile acid malabsorption or bacterial overgrowth could affect the accuracy of mt-sDNA.

To evaluate these concerns, Dr. Ebner and his co-investigators examined medical records from 336 average-risk adults who had undergone BMS at Mayo Clinic between 2014 and 2019 and then had subsequent mt-sDNA within a median 8.9 years after surgery. Most of these patients were white and female, and 81% had undergone Roux-en-Y gastric bypass. Their median body mass index before BMS was 44 kg/m2.

The researchers compared the rates of neoplasia detection during colonoscopy after mt-sDNA with neoplasia detection rates in a group of 139 patients who also had BMS but were screened with colonoscopy alone. These rates were also compared with a historical cohort of 1,542 patients who did not undergo BMS and were screened using mt-sDNA and follow-up colonoscopy.

According to the findings, 14.6% of BMS patients who underwent mt-sDNA had a positive test result. Nearly all of these mt-sDNA–positive patients (96%) then underwent follow-up colonoscopy, and the positive predictive value (PPV) for any neoplasm was 61.7% (95% CI, 46%-75%). The PPV for advanced colorectal neoplasia in particular was 25.5% (95% CI, 14%-40%), the researchers reported.

According to Dr. Ebner’s team, that PPV is similar to the 28% PPV for advanced colorectal neoplasia in the historical cohort of average-risk individuals who had not undergone BMS and were screened at Mayo Clinic using mt-sDNA (P=0.86). In addition, the rate of advanced neoplasia detection during colonoscopy was significantly higher in the group that first had a positive mt-sDNA compared with the group that had BMS and underwent screening colonoscopy alone.

The investigators also reported that the PPV of mt-sDNA in BMS patients was not affected by the presence of iron deficiency or anemia.

The results are limited by the retrospective design of the study and absence of a negative predictive value calculation, but use of two comparison groups addresses some of those limitations, the researchers said.

The researchers concluded that “the performance of mt-sDNA is similar to that observed among average-risk adults and can be reliably utilized for CRC screening.”

—David Wild

The research was funded in part by Exact Sciences, maker of the mt-sDNA test Cologuard.