Primary cerebral myxofibrosarcoma: clinical, morphologic, immunohistochemical, molecular, and ultrastructural study of an infrequent tumor in an extraordinary localization.

Herein, we describe an intracerebral primary low-grade myxofibrosarcoma occurring in a 9-year-old boy. The lesion measured 7 cm and occupied the left parieto-occipital region. A gross-total removal of the tumor was performed. Nine months later, radiologic follow-up revealed a local recurrence which was again surgically removed. The patient then underwent radiotherapy and chemotherapy. He was well and disease-free at 6 months follow-up. The tumor was composed of spindle, stellated, and multinucleated cells embedded in a myxoid background. Foci of increased cellularity, pleomorphism, and high mitotic rate were present. The tumor borders were sharply demarcated from the non-neoplastic nervous parenchyma. Immunohistochemical staining showed that the neoplastic cells were vimentine and CD34 positive. Fluorescence in-situ hybridization analyses did not show FUS and EWSR1 gene rearrangements. Primary intracranial myxofibrosarcomas are very rare (to the best of our knowledge, less than 10 published cases in the international literature). We believe each new case should be recorded to produce a better clinical, pathologic, molecular, prognostic, and therapeutic characterization of this lesion.