Low-grade malignant soft-tissue perineurioma: interphase fluorescence in situ hybridization.

Perineuriomas are usually benign soft-tissue tumors that arise from perineurial cells of the peripheral nerve sheath. Low-grade malignant perineurioma is a rare type of perineurioma, presenting with infiltrative growth, low mitotic activity, and a lack of necrosis. This report describes a case of low-grade malignant perineurioma in a 60-year-old man who presented with a growing tumor on the dorsal side of his left wrist. The tumor was surgically excised and showed no adhesion to the surrounding muscle and no continuity with nerves. There was no evidence of recurrence or metastases 12 months after surgery. Histology indicated that the tumor contained hypercellular and hypocellular areas with spindle-shaped cells proliferating in storiform patterns or perivascular whorling. There was moderate infiltrative growth into the surrounding tissue. There was an evident central infarction but no coagulative necrosis. Mitotic figures were observed at 5/10 high-power fields. On immunohistochemistry tumor cells were found to be positive for epithelial membrane antigen, glucose transporter protein 1, and claudin-1. Approximately 18.4% of tumor nuclei were labelled for Ki-67. Interphase fluorescence in situ hybridization on paraffin sections indicated a loss of chromosome 13. This suggests that chromosome 13 abnormalities could also be involved in perineurioma with low-grade malignant potential.