Cytological Assessment of Metastatic Gastrointestinal Stromal Tumor in Ascitic Fluid.

Gastrointestinal stromal tumors (GISTs) are mesenchymal neoplasms typically arising in the stomach and small intestine and rarely involving extra-gastrointestinal organs. While fine-needle aspiration (FNA) offers reliable diagnosis, exfoliation of GIST cells into body fluids is exceedingly rare and diagnostically challenging. We report a case of a 69-year-old male with metastatic GIST in ascitic fluid. The cells revealed atypical epithelioid morphology with high nuclear-to-cytoplasmic ratio and nuclear irregularities. Immunohistochemistry (IHC) demonstrated positivity for CD117 and DOG1. Diagnosis requires integration of clinical history, cytomorphology, and a broad IHC panel. Awareness of its cytologic features, application of mesenchymal markers, and molecular testing are critical for accurate diagnosis and effective clinical management.