Background:Telomerase activity is up-regulated in pancreatic cancer.Hence,measurement of telomerase activity in pancreatic needle-biopsy specimens could assist in establishing a positive diagnosis in specimens that are inadequate for cytology.Objective:To determine the sensitivity and specificity of telomerase activity for neoplasia in a series of EUS-guided fine-needle aspirate(EUS-FNA)biopsies of pancreatic mass lesions.Design:Prospective,consecutive,nonrandomized cohort.Setting:Academic hospital,tertiary referral center.Patients:Seventy-one patients with a pancreatic mass diagnosed by cross-sectional imaging.Interventions:EUS-FNA of 52 solid and 18 cystic pancreatic lesions.Main Outcome Measurements:(1)Cytologic diagnosis;(2)tissue telomerase activity by semi-quantitative polymerase chain reaction;(3)patient demographics;(4)clinical outcomes.Results:Cytology results were positive for adenocarcinoma in 40 patients with a solid pancreatic mass;of these,telomerase activity was detected in 31.There were no telomerase false-positive results.Telomerase results were positive in 6 of the 7 patients(86%)who had negative cytology results and who eventually were found to have biopsy-proven adenocarcinoma.The sensitivity and specificity of telomerase activity for detecting pancreatic adenocarcinoma in solid masses was 79%(95%CI,64%-89%)and 100%(95%CI,55%-100%).Limitations:Extremely high sensitivity and specificity of EUS-FNA cytology in solid lesions minimized the incremental benefit of telomerase.Conclusions:Telomerase activity can be measured readily in specimens obtained at EUS-FNA and accurately predicts malignancy.Used in combination with cytology,telomerase increased the sensitivity from 85%to 98%while maintaining the specificity at 100%.Lesions with negative cytology result and positive telomerase activity should be evaluated aggressively to exclude malignancy. Background: Telomerase activity is up-regulated in pancreatic cancer .ence, measurement of telomerase activity in pancreatic needle-biopsy tests could assist in establishinga positive diagnosis in specimens that are inadequate for cytology. Objective: To determine the sensitivity and specificity of telomerase activity for neoplasia in a series of EUS-guided fine-needle aspirate (EUS-FNA) biopsies of pancreatic mass lesions. Design: Prospective, con-cutive, nonrandomized cohort.Setting: Academic hospital, tertiary referral center. Patient: Seventy-one patients with a pancreatic mass diagnosed by cross-sectional imaging. Interventions: EUS-FNA of 52 solid and 18 cystic pancreatic lesions. Main Outcome Measurements: (1) Cytologic diagnosis; (2) tissue telomerase activity by semi-quantitative polymerase chain reaction; (4) clinical outcomes. Results: Cytology results were positive for adenocarcinoma in 40 patients with a solid pancreatic mass; of these, telomerase activity was detected in 31.There were no telomerase false-positive results.Telomerase results were positive in 6 of the 7 patients (86%) who had negative cytology results and who eventually found found to have biopsy-proven adenocarcinoma.The sensitivity and specificity of telomerase activity for the detection of pancreatic adenocarcinoma in solid masses was 79% (95% CI, 64% -89%) and 100% (95% CI, 55% -100%). Limitations: Extremely high sensitivity and specificity of EUS-FNA cytology in solid lesions minimized the incremental benefit of telomerase. Conclusions: Telomerase activity can be measured readily in specimens obtained at EUS-FNA and accurately predicts malignancy. Used in combination with cytology, telomerase increased the sensitivity from 85% to 98% while maintaining the specificity at 100 %. Lesions with negative cytology result and positive telomerase activity should be as aggressively to exclude malignancy.