Outcome analysis of childhood pilocytic astrocytomas: a retrospective study of 148 cases at a single institution

Background: Pilocytic astrocytomas (PAs) are characterized by an excellent prognosis although several factors of adverse outcome have been reported. The mitogen-activated protein kinase pathway plays a major role in their tumorigenesis.

Aim: To report a series of 148 PAs in children to define clinicopathological and biological prognostic factors.

Methods: Clinical data were collected from patient files and mail inquiry. Pathological specimens were centrally reviewed. The three major KIAA1549:BRAF fusion subtypes were analysed by reverse transcription - polymerase chain reaction (RT-PCR) in a subset of 47 frozen cases and by fluorescence in situ hybridization on formalin-fixed paraffin-embedded tissue in 23 cases. Tumour location, age at surgery, extent of surgical removal, histological subtype and KIAA1549:BRAF fusion by RT-PCR were searched for prognostic significance.

Results: Pilomyxoid astrocytoma (PMA) and the hypothalamo-chiasmatic (H/C) location were associated with a worse prognosis [P < 0.001 for overall survival (OS) and P = 0.001 for progression-free survival (PFS)]. Patients who underwent complete surgical excision had a better OS (P = 0.004) and a longer PFS (P < 0.001) than the others. Age was also a strong prognostic factor for OS but not for PFS. Infants (<1 year) and young children (<3 years) had a much worse outcome than the others (P < 0.001 and P = 0.004 respectively). KIAA1549:BRAF fusion status was not predictive of outcome.

Conclusion: This study highlights the good prognostic factors of PAs but H/C PA remains a subgroup with dismal prognosis associated with young age, PMA variant and incomplete surgery. Search for KIAA1549:BRAF fusion in tumours with PA pattern is recommended even though the prognostic impact is still unclear.