Interphase cytogenetics of glioblastoma and gliosarcoma

Interphase cytogenetics, i.e., in situ hybridization using probes to chromosome-specific DNA, enables histological identification of cells bearing numerical chromosome aberrations and cytogenetic analysis of composite tumors. We studied routinely processed tissues from seven glioblastomas and three gliosarcomas using biotinylated probes to pericentromeric alpha-satellite sequences on chromosomes 10, 17 and X. By applying various pretreatment protocols, an evaluable compromise between morphology and signal intensity was obtained in most cases. Compared to vascular cells with normal chromosomal counts, a significant subpopulation of glioblastoma cells showed monosomy 10 (four of five cases), monosomy 17 (one of seven cases) and loss of one X chromosome (one of seven cases). All monosomy 10 cases comprised additional areas where two copies of chromosome 10 were retained. Among the gliosarcomas, both the glioma and the sarcoma portion showed monosomy 10 in one case and monosomy 17 in another case. In contrast, in the third case of gliosarcoma, monosomy 10 was found only in the glioma portion, whereas a gain of chromosome X was observed in the sarcoma portion. We conclude that: (1) numerical chromosome aberrations can be detected in routinely processed brain tumor biopsy specimens using interphase cytogenetics, making retrospective studies feasible; (2) glioblastomas show intratumoral cytogenetic heterogeneity with formation of monoclonal cell clusters; and (3) sarcoma and glioma elements in gliosarcomas may exhibit the same or different numerical chromosome aberrations, suggesting various histogenetic pathways of the sarcoma-like portion.