False-positive EUS-guided FNA cytology for solid pancreatic lesions

Background: The currently accepted paradigm is that the false-positive (FP) rate for EUS-guided fine-needle aspiration (EUS-FNA) cytologic analysis of a pancreatic lesion is less than 1%. Objective: To assess the FP rate of EUS-FNA in patients who underwent surgical resection for presumed pancreatic cancer. Design: Retrospective study. Setting: Tertiary-care referral center. Patients: This study involved 367 patients with solid pancreatic lesions in whom EUS-FNA cytology results were interpreted as positive or suspicious for malignancy, which resulted in subsequent surgical resection. Intervention: Surgical resection. Main Outcome Measurements: The FP diagnosis was defined as EUS-FNA cytology specimens being reported as "positive" or "suspicious for malignancy" but that were later proven to be benign on surgical pathology. Results: The FP rate for EUS-FNA was 4 of 367 (1.1%) when only "positive" cytology findings were interpreted as malignant and 14 of 367 (3.8%) when both suspicious and positive cytology findings were interpreted as malignant. Among the 4 cases falsely interpreted as positive, 1 was falsely diagnosed cytologically as a neuroendocrine tumor and 3 as adenocarcinomas. All FP specimens showed chronic pancreatitis on surgical pathology. The incidence of discordance between cytology and surgical pathology did not change over time (2000-2006: 8/188 [4.3%] vs 2007-2010: 6/179 [3.4%]; P =.79). Limitations: Retrospective study at a single center. Conclusion: In a retrospective cohort trial, the FP rate for EUS-FNA of solid pancreatic lesions was 1.1%. Findings of the current study are in line with previous studies that have evaluated the FP cytology rates with EUS-FNA of solid lesions. FP cases transpired primarily as a result of cytologic misinterpretation in the setting of chronic pancreatitis.