Prospective Cytological Assessment of Gastrointestinal Luminal Fluid Acquired During EUS: A Potential Source of False-Positive FNA and Needle Tract Seeding

OBJECTIVES: Endoscopic ultrasound (EUS) fine needle aspiration (FNA) can result in false-positive cytology and can also cause needle tract seeding. Our goal was to evaluate a potential cause, namely, the presence of malignant cells within gastrointestinal (GI) luminal fluid, either as a result of tumor sloughing from luminal cancers or secondary to FNA of extraluminal sites. METHODS: During EUS, luminal fluid that is usually aspirated through the echoendoscope suction channel and discarded was instead submitted for cytological analysis among patients with cancer and benign disease. Pre- and post-FNA luminal fluid samples were collected to discern the role of FNA in inducing a positive cytology. When not performing FNA, one sample was collected for the entire examination. The final diagnosis was based on strict clinicopathological criteria and ≥2-year follow-up. This study was conducted in a tertiary referral center. RESULTS: We assessed the prevalence of luminal fluid-positive cytology among patients with luminal (e.g., esophageal), extraluminal (e.g., pancreatic), and benign disease. Among the 140 patients prospectively enrolled with sufficient sampling and follow-up, an examination of luminal fluid cytology showed positive results for malignancy in luminal and extraluminal cancer patients, 48 and 10%, respectively. This included 8 out of 23 esophageal, 4 of 5 gastric, and 9 of 15 rectal cancers. The positive luminal fluid cytology rate with luminal cancers was not affected by performing FNA. Post-FNA luminal fluid cytology was positive in 3 out of 26 with pancreatic cancers. Cytological examination of luminal fluid aspirates did not demonstrate malignant cells in any patient with nonmalignant disease. CONCLUSIONS :Malignant cells are commonly present in the GI luminal fluid of patients with luminal cancers and can also be found in patients with pancreatic cancer after EUS FNA. Further study is needed to determine the impact of these findings on cytological interpretation, staging, risk of needle tract seeding, and patient care and outcomes.