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AIM:To evaluate the diagnostic characteristics of magnifying endoscopy with acetic acid spray and narrowband imaging(MA-NBI)for early colorectal cancer.METHODS:We conducted a prospective study to evaluate the diagnostic characteristics of MA-NBI in differentiating early colorectal adenocarcinomas from adenomas.To compare the results,we used magnifying endoscopy with NBI(M-NBI)and magnifying endoscopy with crystal violet staining(M-CV).The study was performed in 2 phases.In phase 1,10 colonoscopists at our institution were shown still photographs of 35colorectal polyps(24 adenocarcinomas and 11 adenomas)in M-NBI,MA-NBI,and M-CV.They made diagnostic predictions using a five-grade scoring evaluation.We plotted receiver operating characteristic curves and compared the areas under the curves(AUCs).In phase2,colorectal polyps measuring≥8 mm were prospectively enrolled.During real-time colonoscopy,one ofthe 7 colonoscopists scored the lesion as an adenocarcinoma or an adenoma and assigned a level of confidence to the prediction(high or low).We calculated the accuracy,sensitivity,specificity,positive predictive value(PPV),and negative predictive value(NPV)for each method and compared the proportions of highconfidence predictions.RESULTS:In phase 1,the mean±SD AUCs were 0.64±0.031 in M-NBI,0.71±0.066 in MA-NBI,and 0.76±0.059 in M-CV(P<0.05 for M-NBI vs MA-NBI,P<0.001 for M-NBI vs M-CV,and not significant for MANBI vs M-CV).In phase 2,84 patients with 91 lesions(46 adenocarcinomas and 45 adenomas)were enrolled.The diagnostic characteristics were as follows:73%accuracy,85%sensitivity,60%specificity,68%PPV,and 79%NPV in M-NBI;73%accuracy,80%sensitivity,64%specificity,70%PPV,and 76%NPV in MA-NBI;and 73%accuracy,83%sensitivity,62%specificity,69%PPV,and 78%NPV in M-CV.The proportions of high-confidence predictions were 57%in M-NBI,75%in MA-NBI,and 76%in M-CV(P<0.005 for M-NBI vs MA-NBI,P<0.0005 for M-NBI vs M-CV,and P=1.0 for MA-NBI vs M-CV).CONCLUSION:MA-NBI is useful for differentiating early colorectal adenocarcinomas from adenomas.