Staging and Prognosis

Meeting Abstract

MIB-1 labeling index as a predictor of tumor progression in pilocytic astrocytomas in children and adolescents

D. C. Bowers, P. Kapur, N. J. Winick, L. R. Margraf

UT Southwestern Medcl School, Dallas, TX

Pilocytic Astrocytomas (PA) are a distinct subtype of low-grade glioma and the most common CNS tumor of childhood.
The prognostic importance of the MIB-1 Labeling Index (LI) has not been examined for progression-free survival (PFS) among children with PAs.
Consecutive children from a single institution with a confirmed histologic diagnosis of PA were examined to identify risk factors for subsequent tumor progression.
Immunohistochemistry with the MIB-1 antibody was done according to standard methods.
141 consecutive children with a PA were identified [mean age: 7.6 ± 4.7 years, range: 0.43 - 18.56 years; 78 (55.3%) males].
After a mean follow-up period of 4.45 years, 53 patients have experienced tumor progression (Kaplan-Meier PFS = 61.25% at 5 years).
The average time from diagnosis to progression was 1.3 ± 1.9 years.
By log rank analysis, PAs with an MIB-1 LI of ³ 2.0 had a shortened PFS compared to PAs with a MIB-1 LI < 2.0 (p value = 0.035).
PAs that had complete tumor resections, located in the cerebellum, treated with surgery only had a more prolonged PFS compared to tumors that had incomplete tumor resections, were located elsewhere, and received adjuvant therapy (all p values = 0.001).
Tumors located in the optic pathways had a shorter PFS than located elsewhere (p value = 0.001).
Age at diagnosis and tumors located elsewhere in the brain were not associated with PFS.
By Cox regression multivariate analysis, tumors that were completely resected were less likely to progress than incompletely resected tumors (p = 0.001), and tumors located in the cerebellum were less likely to progress than tumors located in other locations (p = 0.019).
Despite a reputation as a benign tumor, over one third of PAs in children progress.
An MIB-1 LI of ³ 2.0 was associated with an increased frequency of tumor progression.
PAs that are completely resected, and are located in the cerebellum have the best prognosis.
Further work remains to better understand the biology of this relatively common neoplasm, and how it influences clinical progression.

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