Glioblastomatous transformation of ganglioglioma: Case report with reference to molecular genetic and flow cytometric analysis

Gangliogliomas generally behave as benign indolent tumors. However, gangliogliomas undergoing malignant transformation have also been reported. The molecular basis for the malignant transformation of gangliogliomas remains unclear. We describe a case of ganglioglioma, which had transformed to glioblastoma after the gross total resection of the original tumor, in a 4‐year‐old girl. The present case is unusual in four aspects: (i) it arose from a low‐grade ganglioglioma in the absence of previous radiation or chemotherapy, which is the fourth reported case; (ii) the original tumor showed a high proliferative index on flow cytometry but a low Ki‐67 labeling index, implying that the application of flow cytometry might play a certain role in predicting biological and clinical behavior of low grade gangliogliomas; (iii) p53 mutation and deletion appeared in the secondary glioblastoma, which was not shown in the original well‐differentiated ganglioglioma; and (iv) the transformed glioblastoma showed p16 inactivation detected by methylation and deletion, which are relatively uncommon genetic events in secondary glioblastomas. This is the first report of a genetic alteration in glioblastoma arising from a well differentiated ganglioglioma prior to radiation or chemotherapy. Based on the above findings, irrespective of radiotherapy or chemotherapy, rare recurrence of malignant evolution, especially tumors of high S‐phase fraction on flow cytometry, warrants long‐term follow‐up, even in a well‐differentiated ganglioglioma.