Presenter: Joseph Reza MD | AdventHealth Orlando Background: Tumor sizing has prognostic consequences in patients with pancreatic cancer, as larger tumors tend to invade vital structures impeding resection and are associated with higher rates of metastatic lymphadenopathies. Endoscopic ultrasound (EUS) plays a crucial role in the staging of these patients, but findings are directly dependent on the experience of the operator and tumor location. In this study, we compared preoperative tumor sizing measured by EUS to size on pathological specimens in patients that underwent curative-intended resections. Methods: A retrospective review of patients with biopsy proven adenocarcinoma of the head of the pancreas that underwent resection at a tertiary center was performed. Basic demographics were recorded. Maximal tumor dimensions determined by EUS were compared to those found on final pathological reports. Analysis was performed with Pearson correlation test using SAS studio. Results: A total of 97 patients underwent a pancreaticoduodenectomy during the study period. Patients that underwent neoadjuvant therapy for borderline resectable or locally advanced cancer were excluded from the analysis. From the remaining group, 56 patients underwent upfront surgery for resectable disease. Most patients were males, whites, with an average age at diagnosis of 69 years. The total number of harvested lymph nodes was 15 with a positivity rate of 82%; 77% of patients had R0 resections. The average maximal dimension of the tumor calculated by EUS was 2.45 cm, compared to 3.11 cm seen on pathological reports (Pearson correlation coefficient 0.45400, p=0.0004). Conclusion: Endoscopic ultrasonography is commonly used in the diagnostic workup of patients with pancreatic cancer. Based on our results, determination of tumor sizing based on EUS has the potential to under-stage patients with pancreatic cancer.