Fine needle aspiration of gastrointestinal stromal tumors

OBJECTIVE: Gastrointestinal stromal tumors (GISTs) are uncommon mesenchymal tumors of the gastuointestinal tract. Fine needle aspiration (FNA) is one option for diagnosing GISTs before surgery. This study was designed to eval uate the clinical utility of FNA in the diagnosis of GISTs. STUDY DESIGN: FNAs from 19 GISTs originating in the stomach, small bowel an d colon obtained from 1988 to 1998 were studied. Immunocytochemistry was pe rformed on 12 cases. The GISTs were classified as benign, borderline and ma lignant, according to location, size, mitotic activity and clinical outcome . RESULTS: Benign (three) and borderline (five) GISTs were all spindle cell type; malignant GISTs included five spindle cell type and six epithelioid type. Most smears contained abundant cellular material. Benign and border l ine GISTs of spindle cell type tended to have cells arranged in tightly coh esive clusters, while malignant GISTs were more likely to exhibit loosely c ohesive groups with many single cells, occasional nuclear pleomorphism, hyp erchromasia and irregular nuclear contours. Epithelioid-type GISTs mimicked adenocarcinoma. Mitoses were seldom observed in either type CD117 (KIT pro tein product) was demonstrated by immunocytochemistry in 9 cases, CD34 in 1 1, desmin in 3, S-100 protein in 2 and smooth muscle actin in 6 cases CONCLUSION: FNA can be used to diagnose GISTs as spindle cell and epithelio id types, but cytomorphology alone cannot be used to assess malignant poten tial. Immunocytochemical staining for CD117 is helpful in confirming the di agnosis. Care must be taken to differentiate epithelioid-type GISTs from ad enocarcinoma.