A CYTOGENETIC STUDY OF 19 RECURRENT GLIOMAS

A cytogenetic analysis was performed on 19 recurrent gliomas all of wh ich had been treated by radiotherapy. All cases exhibited clonal chrom osomal anomalies, the tumors were classified into four categories in r elation to their mono- or polyclonality and to the presence or absence of a clonal evolution. Polyclonal tumors without clonal evolution had a delay of recurrence significantly longer than monoclonal or polyclo nal tumors with clonal evolution. This difference could be related to the presence of clones with different malignant potential, which could be differentiated by their pattern of chromosomal aberrations. The ma lignant potential of ''highly malignant'' clones resulted from the jux taposition of imbalances, such as monosomy 10, as in high-grade primar y gliomas, and presumably radiation-induced structural rearrangements. That of clones of low malignancy was almost limited to the presence o f multiple balanced structural rearrangements, probably induced by rad iation.