Atypical teratoid/rhabdoid tumor arising in pleomorphic xanthoastrocytoma: A case report

Atypical teratoid/rhabdoid tumor ( AT / RT ) is a rare, highly malignant, true rhabdoid tumor in the central nervous system predominantly presenting in young children. AT / RT typically shows rhabdoid cells which can also be seen in other tumors, but it is differentiated from other tumors by the specific genetic alteration involving the SMARCB1 gene. Only a few cases of AT / RT arising in low‐grade glioma have been reported. A 13‐year‐old girl presented with headache, dizziness, nausea and vomiting. A 4.7 cm cerebellar mass was found on MRI . The mass was totally removed. Histologically, the tumor revealed two distinct morphologic appearances: central areas of AT / RT containing rhabdoid cells and sarcomatous component in the background of pleomorphic xanthoastrocytoma ( PXA ). Immunohistochemically, PXA areas retained nuclear expression of INI ‐1 and low K i‐67 proliferation index, whereas AT / RT component showed loss of INI ‐1 nuclear expression and markedly elevated K i‐67 proliferation index. Epithelial membrane antigen ( EMA ), smooth muscle actin ( SMA ), and p53 protein were positive only in AT / RT . BRAF V600E mutation was identified in PXA by real‐time polymerase chain reaction. We report a rare case of AT / RT arising in PXA which is supposed to progress by inactivation of INI ‐1 in a pre‐existing PXA .