Ahead of Print: Cystic Glioblastoma: IDH1 Status and Prognosis

Background: Controversy exists regarding the prognostic significance of cystic features in newly diagnosed glioblastoma (GBM) and the pathological origin of cystic GBMs.

Objective: To determine whether cystic GBMs develop from low-grade gliomas by evaluating IDH1 status and to evaluate differences in overall survival between patients with cystic and non-cystic tumors.

Methods: We retrospectively reviewed the records of 351 consecutive newly diagnosed adult GBM patients treated at our institution from October 1997 to November 2011; patients with >50% cystic tumor composition were further identified. IDH1 mutation was determined by immunohistochemical staining. Patient characteristics and treatment were reported for cystic and non-cystic tumors separately. Overall survival was reported for cystic and non-cystic cohorts using the Kaplan-Meier estimates.

Results: Of 351 patients, 27 (7.7%) had cystic tumors and 324 (92.3%) had non-cystic. Tumor samples for cystic GBM patients were immunohistochemically analyzed for IDH1 mutations. Two (7.4%) of the 27 tumor samples were documented as having IDH1 mutations. Characteristics such as age, gender, perioperative KPS, tumor size, extent of resection, post-surgery radiation and temozolomide therapy were comparable in the cystic and non-cystic cohorts. Cystic patients had a median overall survival of 15.0 months compared to 18.2 months for non-cystic (log-rank p=0.77).

Conclusion: The low frequency of IDH1 mutation status in our cystic cohort strongly suggests that most newly diagnosed cystic GBMs do not arise from malignant transformation of previously undiagnosed cystic low-grade gliomas. Furthermore, there is no difference in overall survival between cystic and non-cystic newly diagnosed GBM patients.

From: Cystic Glioblastoma: An Evaluation of IDH1 Status and Prognosis by Patil et al.

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