Abstract Sporadic pancreatic ductal adenocarcinoma (PDA) is a highly lethal cancer and with no proven screening strategies. Adnab-9, a monoclonal antibody to constituents of human colonic adenomas has been shown to be prognostic in IPMN and diagnostic in gastric and colorectal cancer or adenomas (CRN). In this study, we retrospectively and prospectively evaluated the diagnostic potential of Adnab-9 in the stool of two distinct PDA populations. Methods: As proof of principle, 249 Chinese patients submitted stool for screening. Retrospectively, 15 patients had PDA and 80 patients without cancer served as controls. Adnab-9 stool reactivity was determined by ELISA. Prospectively, 1132 American CRN screening program patients submitted stool. Six patients developed PDA over five years of follow-up. 11 Patients free of any significant CRN or other cancer but deceased due to other causes, served as controls. An additional four patients with a known family history of PDA also prospectively submitted stool for Adnab-9. Results: The prospective study results are summarized in the Table. Table: Prospective Study Data for Adnab-9 stool antibody as a biomarker of PDA. The pilot study in Chinese PDA patients found that 12 of 15 patients had stool Adnab-9 ELISA positivity compared to 10 of 80 controls (OR 28, CI 6.7-116.8, P<0.0001). 4 of 6 prospective American study PDA patients had either stool ELISA or Western blot positivity for Adnab-9 compared to 1 of 11 controls (OR=20, CI 1.4-287.6, P<0.03). 2 of 4 patients with family history of PDA had stool positive by Adnab-9 ELISA or Western blot. Conclusions: Our study suggests that Adnab-9 stool tests may be an effective PDA diagnostic marker. Based on previous data in CRC and IPMN, Adnab-9 appears to bind Paneth-like cells, which we and others have shown to be cancer-associated and the likely source of the stool antigen. Future prospective studies are needed to confirm the diagnostic efficacy of Adnab-9 stool testing in PDA. Citation Format: {Authors}. {Abstract title} abstract. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3699. doi:1538-7445.AM2012-3699