MULTINUCLEATED GIANT STROMAL TUMOR OF THE OMENTUM - REPORT OF A CASE WITH IMMUNOHISTOCHEMICAL AND ULTRASTRUCTURAL INVESTIGATION

Multinucleated giant stromal cells (MGSC) have been described in a var iety of lesions of various anatomical sites. They are generally believ ed to be derived from fibroblasts or myofibroblasts. Their size and bi zarre appearance may lead to an erroneous interpretation of infiltrati ng malignant cells, but they are regarded as reactive in nature. MGSC also seem to participate in a neoplastic process and form a part of tu mors called giant cell fibroblastomas (GCF). In GCF, multinucleated gi ant cells are sparsely scattered throughout the tumor, which is compos ed of loosely arranged spindle cells. Thus far, no tumor composed of M GSC entirely, to the best of the authors' knowledge, has been reported . This study involved an 80-year-old female with an omental tumor, whi ch is believed to represent the first case of tumor of MGSC. The patie nt developed abdominal pain; a large abdominal tumor measuring 18 x 15 x 5 cm by computerized tomography was found located between the left lobe of the liver, the transverse colon, and the greater curvature of the stomach. Although the tumor was adherent to the above organs and i nfiltrating the omentum, it was resectable. Grossly, the tumor was hig hly vascular and the surface was shaggy with no recognizable capsule. The cut surfaces were red to tan with frequent cystic spaces containin g bloody material. Microscopically, the tumor cells were large and mul tinucleated (2-6 nuclei) with prominent nucleoli. The cytoplasm was ab undant and stained amphophilic. These tumor cells formed moderately ce llular sheets filling the spaces between the varying sized vessels. Th ere was prominent vascularity throughout the tumor. DNA study by image analysis revealed aneuploidy peaks. On immunohistochemistry, the tumo r cells were strongly positive for vimentin, moderately positive for a ctin along the periphery of the cytoplasm, and negative for cytokerati n, EMA, myoglobin, S-100, CEA, Factor Xllla, HMB-45, and HAM56 and KP- 1. Ultrastructurally, the cytoplasm contained rich profiles of RER wit h scattered lysosomes. The cell borders were slightly irregular with o ccasional subplasmalemmal densities facing loosely arranged collagenou s stroma. The light microscopic, immunohistochemical, and electron mic roscopic features of tumor cells were remarkably similar to MGSC. The tumor size and gross appearance suggested a malignancy, but it was a d iploid tumor and the patient remains disease free 5 years after a comp lete resection.