CNS tumor with BCOR internal tandem duplication: Clinicopathologic, molecular characteristics and prognosis factors.

The central nervous system tumor with BCOR internal tandem duplication (CNS tumor with BCOR ITD) is a recently identified rare tumor entity, the complete morphologic characteristic, genetic alteration, classification, clinical outcomes and optimal treatment for this tumor entity have not been fully clarified. Here, two new cases of CNS tumor with BCOR ITD were reported and the clinicopathologic, molecular characteristics, and prognosis were analyzed through reviewing of the reported literature. The histological features included a clear border with adjacent brain parenchyma, an extensively microcystic background, and the cells with round to oval nuclei containing delicate chromatin, ependymoma-like perivascular pseudorosettes, and palisading necrosis. Immunohistochemical features showed strong and diffuse positive expression for BCOR, scattered positive expression for OLIG2, and negative expression for GFAP, Syn, and EMA. PCR and direct DNA sequencing analysis identified exon 15 ITD of the BCOR gene in both cases. Interestingly, both cases revealed two duplication segments, which had not been reported in the literature. A review of the literature shows that CNS tumor with BCOR ITD has a poor prognosis with a median survival of 1.7 years; surgical gross total resection is a good prognostic factor. A combination of radiation treatment and chemotherapy, while trending towards significance, does not reach statistical significance. On the contrary, the OS is not associated with age, gender, and tumor location. In conclusion, CNS tumor with BCOR ITD is a rare tumor entity with characteristic morphologic and molecular features and a poor prognosis. The optimal treatment strategies need further studies.