Background: Endoscopic Ultrasound (EUS) is considered the best modality for the locoregional staging of all gastrointestinal(GI) luminal cancers. No studies have investigated the possibility of false-positive lymph node FNA in patients with GI cancers or the potential for malignant cell carry-over and needle contamination. Endoscopes that traverse a luminal tumor (LT) may cause cancer cells to shed and contaminate the endoscope tip and the biopsy channel. This may result in false-positive cytology of an aspirate obtained from a sampled lymph node. Our primary aim was to determine if malignant cells carry-over and contaminate the (EUS) endoscope or FNA needle with passage of an endoechoscope through a LT. Methods: In this pilot study, we recruited 16 subjects who were referred for preoperative staging of gastrointestinal cancers; 13 patients with LT (esophageal cancers or gastric cancers) and 3 subjects for a control-arm with non-LT. All patients underwent a radial EUS for preoperative staging. A linear endoechoscope was then passed into their esophagus and stomach to perform either a sham FNA and when indicated a FNA for staging. Cytology samples were taken from the FNA needle, scope channel (brushings of and debris from the channel for cell block and histology), and the scope tip exterior. Direct tumor sampling was obtained for a control. Two blinded pathologists, with expertise in cytologic interpretations, read all slides. Results: Luminal cancers included 10 esophageal cancers, and 3 gastric cancers. Non-LT were pancreatic(2) or lung cancer(1). Of 13 luminal cancers, 7 (54%) had tumor cell carry-over detected by cytologic or histologic interpretation. Four(30%) had cell carry-over onto the cytology brush, 4 (30%) on the exterior scope, 4 (30%) from the cell block, and 2 (15%) from the FNA catheter tip. 29 percent of all patients with tumor cell carry-over had malignant cells found on the FNA needle. The 3 non-LT had no cell carry-over and all had negative controls. Conclusions: 1. Malignant cell contamination of endoechoscopes and FNA needles does occur when staging luminal cancers. 2. The FNA needle can be contaminated with tumor cells prior to obtaining non-peritumoral lymph node cytology, and has potential for false positive aspirates. 3. Endoscopist should be aware of the risks.