Malignant cell contamination may lead to false-positive findings at endosonographic fine needle aspiration for tumor staging.

BACKGROUND AND STUDY AIMS: Endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) of lymph nodes is used for staging of gastrointestinal malignancies. False-positive rates of 5 % - 7 % are not well understood. Elements of EUS examinations that contribute to false-positive cytological findings were investigated. PATIENTS AND METHODS: 13 patients undergoing EUS staging of gastrointestinal luminal malignancy were consecutively enrolled together with 3 patients with extraluminal tumors (pancreas, lung) defined as controls. After EUS, cellular debris and fluid were collected from the FNA needle catheter, instrument channel, and endoscope tip for cytologic and histologic investigation. RESULTS: 6 of 13 patients (46 %) had malignant cells contaminating the FNA needle catheter, instrument channel, or endoscope tip. Malignant cells were present in the instrument channel in 5 cases (38 %), exterior tip of echoendoscope in 4 (31 %) and needle catheter in 2 (15 %). CONCLUSIONS: Echoendoscopes used for FNA in patients with luminal tumors are at risk for malignant cell contamination of the instrument channel, FNA needle catheter, and echoendoscope tip. FNA needle contamination can contribute to false-positive findings.