Malignant transformation of pleomorphic xanthoastrocytoma and differential diagnosis: case report

Pleomorphic xanthoastrocytoma (PXA) is a rare astrocytic glioma, characterized by large pleomorphic and frequently multinucleated cells, spindle and lipidized cells, a dense pericellular reticulin network, and numerous eosinophilic granular bodies according to the grade II glial tumor standards of the World Health Organization's (WHO) 2016 guidelines. PXA rarely transforms into anaplastic PXA or glioblastoma (GBM) and anaplastic PXA, classified as WHO grade III, has a more aggressive clinical behavior with poorer prognosis than PXA.

Here we describe an unusual case of PXA in a 19-year-old woman, first admitted with headache and a mass in the left temporal lobe in 2005 that was removed. Twelve years later, she returned with left temporal headache, diplopia and tinnitus. A local tumor recurrence was found, and a second resection was performed. The specimen showed highly malignant findings, such as necrosis, microvascular proliferation, and multiple mitoses. The integrated diagnosis was made as high grade glioma, probably derived from PXA. Immunohistochemical (IHC) stains were positive for oligo2, and approximately 21% positive for Ki-67, while negative for CD34, IDH1 R132H. INI1 and ATRX were retained. As the histological classification was glioblastoma, the patient received GBM-appropriate chemotherapy and radiation therapy and outpatient follow-ups have demonstrated no obvious symptoms for 1 year after surgery. Additional molecular analyses found BRAF V600E mutations in both resections, supporting the idea that the recurrent tumor had derived from PXA.

This case highlights the complexities of differential diagnosis based on the World Health Organization's 2016 guidelines. More integrated criteria to differentiate anaplastic PXA from GBM and epithelioid GBM, combined with genetic screening results, might be needed.