Proliferative Index in Pediatric Pilocytic Astrocytoma by Region of Origin and Prediction of Clinical Behavior

Background/aims: Pilocytic astrocytomas are common pediatric tumors. Molecular profiles vary with location of origin. Comparisons of proliferation have not been reported. We sought to identify differences in growth by region and whether these predict clinical behavior.

Methods: A retrospective review of all patients undergoing surgery for a pilocytic astrocytoma at Children's Hospital LA from 2003 to 2015 was completed. Tumor location, determined by imaging, was stratified into infratentorial, supratentorial, or optic pathway. Proliferation was measured by Ki-67 immunostaining. A p value of 0.05 was deemed significant.

Results: 77 patients were identified. 51 had posterior fossa tumors, 12 had supratentorial tumors, and 14 had optic pathway tumors. Mean Ki-67 score was 3.67, 4.09, and 3.83%, respectively (p = 0.82). Ki-67 of ≥4% trended towards recurrence (p = 0.11), incomplete resection (p = 0.15), and younger age at presentation (p = 0.04). Ki-67 was weakly correlated with shorter survival after surgery (r = -0.103, p = 0.41). Partial resection strongest predicted recurrence (p < 0.001; OR = 13.0).

Conclusion: Proliferative index does not change by location. Higher cell proliferation was seen in younger patients and associated with shorter time to and a higher risk of recurrence. Further study is needed to identify predictors for clinical behavior. Importance of Study: This study provides a detailed analysis of the proliferative indices of tumors arising from characteristic locations within the brain. With recent advances in our understanding of the differences in molecular and genetic profiles despite similar histologic diagnoses, we felt that it was important to review whether there were unique components of tumor behavior that could be identified. In turn, we sought to determine whether tumor behavior could be used to predict the clinical course. This knowledge is important, given that not every tumor may undergo complete surgical resection, and that some lesions may require more aggressive upfront adjuvant therapy or be closely monitored for recurrence.