HGNET-BCOR Tumors of the Cerebellum: Clinicopathologic and Molecular Characterization of 3 Cases.

The central nervous system (CNS) high-grade neuroepithelial tumor with BCOR alteration (CNS HGNET-BCOR) is a recently described molecular entity. We report 3 new CNS HGNET-BCOR cases sharing common clinical presentation and pathologic features. The 3 cases concerned children aged 3 to 7 years who presented with a voluminous mass of the cerebellum. Pathologic features included proliferation of uniform spindle to ovoid cells with fine chromatin associated with a rich arborizing capillary network. Methylation profiling classified these cases as CNS HGNET-BCOR tumors. Polymerase chain reaction analysis confirmed the presence of internal tandem duplications in the C-terminus of BCOR (BCOR-ITD), a characteristic of these tumors, in all 3 cases. Immunohistochemistry showed a strong nuclear BCOR expression. In 2 cases, local recurrence occurred within 6 months. The third case, a patient who received a craniospinal irradiation after total surgical removal followed by a metronomics maintenance with irinotecan, temozolomide, and itraconazole, is still free of disease 14 months after diagnosis. In summary, CNS HGNET-BCOR represents a rare tumor occurring in young patients with dismal prognosis. BCOR nuclear immunoreactivity is highly suggestive of a BCOR-ITD. Whether CNS HGNET-BCOR should be classified among the category of "embryonal tumors" or within the category of "mesenchymal, nonmeningothelial tumors" remains to be clarified. Because CNS HGNET-BCOR share pathologic features and characteristic BCOR-ITD with clear cell sarcoma of the kidney, these tumors may represent local variants of the same entity.