ACTR-77. DURABLE RESPONSE TO BEVACIZUMAB IN ADULTS WITH RECURRENT PILOCYTIC ASTROCYTOMA

Adult pilocytic astrocytomas (APA) are rare tumors with a more aggressive clinical course when compared to juvenile pilocytic astrocytoma (JPA). Recurrence rates for APA have been reported from 30–42%. APA are known to be highly vascular tumors and we hypothesized that they may be uniquely responsive to bevacizumab (BEV). We present a series of four consecutive adult patients with pathologically diagnosed WHO grade I pilocytic astrocytoma who had a robust and durable response to BEV at time of recurrence. Median age at diagnosis was 34 years (range: 23–66). Three tumors were located infratentorially and one in the thalamus. Three patients underwent a partial resection or near total resection and one patient underwent biopsy only. BRAF v600E mutation was absent in all patients. Ki-67 proliferation index was 5–9%. Initial treatment was radiation alone in 3 patients and concurrent radiation and temozolomide (TMZ) in one patient. All patients developed radiographic changes on MRI, including disease outside the radiation field, that were consistent with progressive disease based on RANO criteria. Median time to recurrence was 8.5 months (range: 4–10 months). All patients were treated with 6 cycles of BEV for recurrence and at the end of treatment, all patients had achieved a complete response. 1 patient also received adjuvant TMZ. Median follow-up time after BEV is 20.5 months (range: 7–34) and as of last follow up, no patient has recurred. Although, BEV has failed to demonstrate a survival benefit to date in all gliomas, this series suggests that BEV may have true anti-tumor activity in APA. Recurrence in APA in this series is consistent with previous reports and BEV may be an important agent to achieve durable disease control. Future multi-center studies to further assess efficacy are warranted.