249 Is Stool DNA Test More Specific for Proximal or Distal Neoplasia?

INTRODUCTION: A handful of studies evaluated stool DNA test as a screening method but there is little to no data on the location of the “positive findings” detected on subsequent colonoscopy. In our study, we performed a retrospective analysis on location of adenoma in patients with positive stool DNA test. METHODS: A retrospective chart review of 459 patients who had a positive stool DNA followed by “positive findings” on subsequent colonoscopy was performed. “Positive findings” was defined as finding of cancerous or advanced precancerous lesions. Only the location of the index lesion was recorded. If two positive findings were recorded, the larger of the two lesions was designated as the index lesion unless they share the exact characteristics. In that case, it was reported as “both proximal and distal.” Proximal colon lesion was defined as lesion noted in the splenic flexure and all the segments proximal to the splenic flexure. Distal colon lesions were defined as lesions distal to splenic flexure. Advanced adenoma was defined as an adenoma that is larger than 10 mm or had high risk features such as villous transformation or high grade dysplasia. Non-advanced adenoma was defined as an adenoma that is smaller than 10 mm and had no high-risk features. RESULTS: Out of the 459 patients, 24 patients had “adenocarcinoma,” 334 patients were noted to have an “advanced adenoma” and 101 patients who had “non-advanced adenoma.” Out of the 24 cancer patients, 70.83% had distal cancer, while 25% had proximal cancer. Interestingly, one patient had a proximal and distal cancer at the same time. The distribution of advanced adenomas was different and the location was shared equally between proximal and distal in 47.31% and 49.40% respectively, while the remaining 3.29% had advanced adenoma in the proximal and distal colon simultaneously. Among patients with non-advanced adenoma, 62.38% of the adenomas were proximal, 26.73% were distal while 10.89% of the patients had evidence of non-advanced adenoma in both proximal and distal colon. CONCLUSION: The location of the “positive findings” on colonoscopy following a positive DNA test varied significantly based on the final diagnosis. Among patients with positive fecal DNA test, more significant pathology such as an advanced adenoma or adenocarcinoma was noted to be in the distal colon.