S2237 High Yield for Molecular Analysis on Cytologic Samples Using a 25-Gauge Core Needle in Malignant Lesions

Introduction: Endoscopic ultrasound (EUS)-guided tissue acquisition provides a malignant diagnosis via either cytology or histology. Various EUS-needle tip designs allow for EUS fine needle aspiration (FNA) and fine needle biopsy (FNB) and are used to diagnose gastrointestinal malignancies. To facilitate personalized oncologic therapy, molecular analysis can be further conducted on the obtained specimens, from either a cytology slide (as in rapid on site evaluation, ROSE) or a formalin-fixed pathology. Previous studies comparing cytology with histology for molecular analysis have yielded mixed results. Nevertheless, cytologic analysis offers distinct advantages, including the potential for ROSE. This study aims to assess the yield of cytology using FNB “core” needles in obtaining molecular marker information. Methods: Adult patients who underwent EUS sampling of various malignant lesions with a fork-tip core needle between January 2015 to January 2025 were included for review. Samples that were sent for cytology and molecular analysis were identified in a database. Demographics and procedure-related factors were retrospectively collected via chart review. Cases in which samples were not acquired via EUS at our center were excluded from the analysis. Results: A total of 127 patients underwent EUS sampling of a mass that was sent for cytology and molecular analysis. Five patients were excluded due to missing a portion of the procedure data. The majority (111/122; 91.1%) used a 25-gauge core needle. The number of passes ranged from 1 to 10, with a median of 3 passes and a mean of 3.5 passes. The most common site for tissue acquisition was the pancreas. Notably, all 122 cytology samples yielded adequate sample for diagnosis and additional molecular analysis. Conclusion: Our study demonstrates that when a core needle is used to obtain cytology sample, if the sample was sufficient to make the malignancy diagnosis on site, this was also 100% adequate for molecular analysis. In addition to demonstrating its efficacy in obtaining adequate sample, our study also highlights that using a smaller, 25-gauge core needle was sufficient for molecular profiling. EUS sampling with a 25-gauge core needle for cytology sample is an effective and sufficient method for both diagnosis and molecular profiling.