trials most enrolled patients underwent systematic, four-quadrant, sampling to characterize patients’ baseline histologic grade prior to therapy. Because of the availability of these level-specific pathological readings, the proximal-to-distal spatial distribution of dysplasia could be characterized for most patients. We performed logistic regression with auto-regressive generalized estimating equations (GEE) to assess patterns of dysplasia, both stratified by trial and pooled, using location measurements statistically standardized to the extent of BE. In this schema, dysplasia at the top of the BE segment was assigned a value of 1, dysplasia at the bottom of the BE segment was assigned as 0, and dysplasia in the middle of the segment was assigned 0.5. Results: Of 140 patients randomized in the SURF trial, 114 had adequately detailed information regarding location of dysplasia, and were included in the analytic subset. Of 127 patients randomized in the AIM-Dysplasia trial, 55 had adequately detailed reports of baseline endoscopy. In both the AIM-Dysplasia trial (OR Z 7.98, 95% CL: [3.13, 20.4]) and the SURF trial (1.97, 95% CL: [1.02, 3.83]) dysplasia was more common at the top of the Barrett’s segment than at the bottom. In the pooled analysis, for every quarter of the segment more proximal, there was an absolute increase in risk of dysplasia of 0.07 [0.03, 0.10].Thus, on average, dysplasia was approximately 21% more common in the proximal-most quartile of BE length compared to the distal-most. The pooled, mean, standardized location of dysplasia was 0.63 [0.59, 0.67]. Discussion: In baseline biopsies from two multicenter, randomized, controlled trials the yield for dysplasia was highest in the proximal area of the Barrett’s segment. Surveillance sampling strategies over-sampling the most proximal areas of the BE segment would thus be expected to have increased yield of dysplasia compared to current standard of care, randomly distributed biopsies. Figure 1. Classification and Statistical Standardization of Biopsy Locations; Biopsy Location is defined as the Length B Divided by the Length A. Figure 2. Estimated prevalence of dysplasia among proximal to distal sampling levels pooled between the AIM-dysplasia and SURF trials. www.giejournal.org Vol Tu1533 Esophageal Posterior and Right Wall Are the Most Common Localizations of Barrett’s Esophagus Stefano Bibbo, Gianluca Ianiro*, Lucio Petruzziello, Cristiano Spada, Alberto Larghi, Maria Elena Riccioni, Antonio Gasbarrini, Guido Costamagna, Giovanni Cammarota Internal Medicine and Gastroenterology Division, “A. Gemelli” University Hospital, Rome, Italy; Digestive Endoscopy Unit, “A. Gemelli” University Hospital, Rome, Italy Background and Aim: Barrett’s esophagus (BE) prevalence is higher in patient with GERD with a rate of 10%, and an associated cancer risk of 0,5%/year. So, careful endoscopic surveillance assumes a paramount importance. Only few literature data on the preferred esophageal location of BE are available to date. The aim of this study is to identify the preferred area where BE can develop within esophageal circumference. Material and Methods: We retrospectively analyzed patients with BE who underwent upper endoscopy between January 2010 and March 2014 at our Endoscopy Center. We included only patients with short BE. In the case of multiple BE tongues, each lesion was considered individually. The circumferential localization of the lesions was determined according to the numbers of a clock face. Results: In the study period, 204 subjects were newly diagnosed of BE or had an endoscopic follow-up of BE. 24 patients with circumferential lesions were excluded. Among the 180 remaining patients, multiple BE lesions were diagnosed in 110 of them, for a total amount of 332 areas of BE. Our analysis of data showed a clear prevalence of BE in the position near 3 o’clock and 6 o’clock of the endoscopic image. The area between 5 and 7 o’clock (posterior wall) was the most affected (38.25% of the lesions). Other localizations were the arc between 2 and 4 o’clock (right wall) with 27.71%, the arc 11 to 1 o’clock 23.80% (anterior wall) and the arc 8 to 10 o’clock 10.24% (left wall). For each of the four walls, difference between observed and expected (dividing equally the number of lesions for the number of quadrants) lesions was statistically significant (P!0.0001 for each wall). Lesions were preferrably located in the right (1 to 6 o’clock) than in the left (7 to 12 o’clock) quadrant (207 versus 125 two-tailed P valueZ 0.01). Conclusions: We found, in a large cohort of Italian patients, an uneven localization of BE in the distal esophagus, with an higher prevalence on the posterior-right wall. Anatomical and environmental factors could explain this finding. The circumferential asymmetry of LES pressure (in particular, a lower pressure on the right quadrant) and the preference of supine position during sleep are two situations that may promote the reflux of gastric fluids preferably in the right and posterior wall of the distal esophagus. A more accurate observation of such areas during endoscopic surveillance is advisable in GERD patients.