Gastrointestinal stromal tumor in ascitic fluid. A case report

BACKGROUND: There are few published data on the cytologic features of gastrointestinal stromal tumors (GISTs) in ascitic fluid and whether these features may mimic those of other malignancies. CASE: An 80-year-old woman presented with ascitics associated with multiple intraperitoneal masses. Cytologic examination of the ascitic fluid showed numerous three-dimensional clusters of epithelioid cells. These features and the presence of large, intracytoplasmic vacuoles raised a possible diagnosis of adenocarcinoma. However, mucin could not be demonstrated in the vacuoles, and the cells showed immunoreactivity for vimentin and c-kit but not for cytokeratins. Eighteen months earlier the patient had undergone a partial gastrectomy for a GIST, which predominantly comprised vacuolated, epithelioid cells. The immunoprofile of the primary tumor was identical to that of the ascitic fluid cells. CONCLUSION: GIST cells may closely mimic adenocarcinoma cells in ascitic fluid. Distinguishing between the two neoplasms has important clinical repercussions and is aided by histochemical and immunocytochemical studies--in particular, c-kit immunostaining.