MN1 rearrangement in astroblastoma: study of eight cases and review of literature.

Astroblastomas are unique tumours with unresolved issues in terms of their origin, molecular biology, clinical behaviour, and response to treatment. To decipher the characteristics of this tumour, we reviewed cases histologically diagnosed as astroblastoma in our institute over the past 8 years, with immunohistochemistry, and performed fluorescence in situ hybridisation (FISH), for the newly emerged MN1 rearrangement which was reported in central nervous system high-grade neuroepithelial tumours. The mean age at diagnosis was 18.6 years with all cases seen in females and with supratentorial localisation. The tumours showed typical circumscription and bubbly appearance on imaging. The cohort included eight cases diagnosed as astroblastoma (two low grades; six anaplastic) based on histology and proliferative index. The tumours displayed characteristic astroblastic pseudorosettes with hyalinised vascular core and variable immunopositivity for glial fibrillary acidic protein, pan cytokeratin, and epithelial membrane antigen. MN1 break-apart by FISH was found in 5/8 of our cases (62.5%), which included 2 low-grade and 3 anaplastic tumours. Tumour recurrence was noted in three cases, with MN1 alteration in two. We account for one of the few series to study the MN1 rearrangement in astroblastoma and conclude that MN1 alteration is seen in a subset of these tumours.