287 The Effect of Smoking on Multitarget Stool DNA Testing

INTRODUCTION: There is a known association between smoking and the development of colorectal cancer. Newer screening tools for colorectal cancer including multitarget stool DNA testing may have differing results with regards to patients who smoke. To our knowledge, there have not been other studies looking at smokers who completed stool DNA testing. Our study was completed to evaluate the effect of smoking on stool DNA testing and subsequent colonoscopy. METHODS: A total of 19400 patients had multitarget stool DNA tests. There was 8448 who did not have the test, and 9008 tests completed had negative results. There were 1413 patients with positive stool DNA followed by documented colonoscopy. Patients with unknown smoking status or finding of other carcinoma aside from adenocarcinoma were excluded. Colonoscopy findings were recorded and were divided into smokers (former or current) and nonsmokers. Only the index lesion was recorded. Advanced adenoma was defined as an adenoma larger than 10 mm or had high risk features such as villous transformation or high grade dysplasia. Nonadvanced adenoma was defined as an adenoma smaller than 10 mm and had no high risk features. Advanced neoplasia was defined as adenocarcinoma or advanced adenoma. Statistical analysis with Chi-square was done to compare the proportions. A P-value < 0.05 was considered statistically significant. RESULTS: Among smokers, 5474 (54%) completed the stool study versus 5474 (59%) among nonsmokers (P < 0.01). The stool DNA test was positive in 1204 (22%) of the smokers versus 738 (13%) (P < 0.01). From the positive results, colonoscopy was completed in 896 (74%) of smokers versus 564 (77%) (P = 0.311). Follow-up colonoscopy yielded 16 (1.85%) adenocarcinomas in the smoking group versus 8 (1.47%) nonsmokers (P = 0.59), 285 (33%) advanced adenomas versus 149 (27%) (P = 0.025), 248 (29%) nonadvanced adenoma versus 168 (31%) (P = 0.395), and 315 (36%) with no adenoma versus 220 (40%) (P = 0.141). A total of 301 (35%) of smokers with a positive test had an advanced neoplasia versus 157 (29%) in nonsmokers (P = 0.02). CONCLUSION: From our study, there is an increased chance of a positive multitarget stool DNA test in smokers as well as a higher chance of finding advanced neoplasia. Further prospective studies are needed to validate patient characteristics for those being offered multitarget stool DNA testing. Smokers may benefit from more immediate colonoscopy given an increased risk of advanced neoplasia in lieu of other screening tools such as stool DNA testing.