Pilocytic astrocytomas in adults: A retrospective study of 125 patients.

2022Background: Pilocytic astrocytomas (PAs) are rare primary brain tumors in adults. The natural history is poorly defined with the largest published series including only 30-40 patients. To better define clinical characteristics of adult PAs, we present an analysis of adult PAs at MD Anderson Cancer Center. Methods: We conducted an IRB-approved, retrospective chart review of patients ≥18 years diagnosed with PAs from 1990-2011 at our institution. Results: We identified 125 patients with a median age of 29 (range 18-72y), female to male ratio of 1.7:1, and median follow-up of 62 months. The most common anatomic locations were brainstem 22%, cerebellum 14%, intraventricular 14%, and cortical/lobar 14% (36% other locations). 21% of cases had an initial pathologic diagnosis discordant with neuropathologic review at our institution. Comorbidities included neurofibromatosis type 1 (5 pts) and a history of asthma or autoimmune disease (14%). 38 patients had a gross total (GTR), 55 a sub-total resection (STR) and the remainder a biopsy. 62 patients were treated with radiotherapy (RT): 45 as adjuvant (adj), 17 at recurrence; 2 received RT in both adj and recurrent settings. 73 (58%) patients were stable after initial treatment (surgery +/- adj RT). Median progression free survivals (mPFS) based on upfront treatment as follows: GTR only (n=30) - not been reached, STR only (n=32) 226.6 months, GTR plus adj RT (n=8) 13.2 months, STR plus adj RT (n=23) is 52.4 months (p=0.026, logrank test for trend). At last follow-up, 77% of all patients were stable and 13% were deceased. Conclusions: This is the largest series of adult PAs reported to date. Extracerebellar location, slight female predominance, and history of allergic/autoimmune disease were associations found in this cohort. Neuropathologic review is essential to avoid misdiagnosis. A significant subset of adult PAs behave more aggressively than expected for a grade I tumor with over 40% of patients experiencing recurrence after initial treatment. Adj RT following GTR or STR did not improve PFS, and a trend towards worse PFS with adj RT was observed although these analyzed subgroups were small. These results may help provide a framework for prospective studies in this tumor type.