NONRANDOM CHROMOSOMAL GAINS IN PILOCYTIC ASTROCYTOMAS OF CHILDHOOD

Low-grade astrocytomas are the most common central nervous system (CNS ) tumor occurring in the pediatric age group. Although many of these t umors are karyotypically normal, various studies have reported gains o f chromosomes in a significant proportion of cases. We had the opportu nity to karyotype two pilocytic astrocytomas occurring in 5- and 15-ye ar-old children. These tumors were characterized by stemlines of 49,XY , +4, +7,+8 and 48,XX, +7, +8. Using these patients as index cases and based on additional karyotypic data that have been published, we perf ormed fluorescence in situ hybridization on 25 additional cases of low -grade astrocytomas in children using pericentromeric probes for chrom osomes 4, 6, 7, 8, 9, 10, 11, 12, 15, and 17. Six of 18 (excluding the two index cases), or one third, of the pilocytic astrocytomas were ch aracterized by chromosomal gains, most commonly chromosomes 7 and 8, s uggesting that trisomy 7 and 8 are relatively common events in the tum origenesis of pilocytic astrocytomas. In contrast, chromosomal trisomi es were not detected in seven well-differentiated fibrillary astrocyto mas with any of the probes chosen. Copyright (C) 1995 by W.B. Saunders Company