MALIGNANT GRANULAR-CELL TUMOR - REPORT OF A CASE AND REVIEW OF THE LITERATURE

The histological, immunohistochemical and electron microscopic feature s of a rare malignant granular cell tumor (GCT) arising in the left ra dial nerve of a 54-year-old man are reported. Despite a lack of local recurrence following extirpation, the tumor metastasized to the skull five years later. Light-microscopically, both primary and metastatic t umors consisted of markedly atypical or pleomorphic neoplastic cells w ith abundant cytoplasm containing diastase-resistant periodic acid Sch iff reaction-positive granules. These tumor cells were arranged in a s heet-like pattern with mitotic figures including atypical ones, and we re frequently immunopositive for proliferating cell nuclear antigen an d c-MET, the c-met proto-oncogene product. These findings reflect high -grade malignancy of the present tumor. In addition, the tumor cells w ere positive for S-100 protein and neuron-specific enolase. Ultrastruc turally, a large number of intracytoplasmic granules featuring seconda ry lysosomes as well as long interdigitating cytoplasmic processes, in tercellular intermediate junctions, discontinuous basal lamina-like st ructures, and stromal long-spacing collagen were observed. These findi ngs indicated schwannian differentiation of the present tumor. In addi tion, based on a review of previously reported cases, the overall clin icopathological characteristics of malignant GCT were summarized.