Rapid postradiation malignant transformation of a pilocytic astrocytoma in an adult with neurofibromatosis type 1: illustrative case.

backgroundJuvenile pilocytic astrocytoma (JPA) is the most common primary brain tumor of childhood and is rarely seen in adults. Neurofibromatosis type 1 (NF1), a common tumor predisposition syndrome, demonstrates a strong association with low-grade gliomas, most notably pilocytic astrocytoma, which are relatively indolent. Unlike its juvenile counterpart, reports of adult pilocytic astrocytoma (APA) vary widely in terms of disease progression from benign to much more malignant courses. Moreover, current studies discussing APA report different treatment approaches and outcomes (e.g., malignant transformation of JPA and APA with or without radiation), as little is known regarding the management of recurrent tumors and how adjuvant therapies may alter disease progression. OBSERVATIONS: The authors report the unique case of an adult male with NF1 and APA who underwent rapid malignant conversion after intensity-modulated radiation therapy. LESSONS: The authors demonstrate that caution should be taken in utilizing radiotherapy instead of resection in cases of APA and NF1, with close monitoring for posttreatment recurrence. https://thejns.org/doi/10.3171/CASE24241.