Detection of chromosomal changes by interphase cytogenetics in biopsies of recurrent astrocytomas and oligodendrogliomas.

Recently, lineage-specific genetic pathways of tumor progression have been suggested in both oligodendrogliomas and astrocytomas. Aberrations consistently reported in gliomas include chromosomes 1, 7, 10, 17 and 19. Identification of specific genetic damage may have important clinical consequences, because oligodendrogliomas, unlike astrocytomas, are responsive to chemotherapy. Genetic alterations specific for tumor type and tumor progression were investigated in 5 pairs of recurrent astrocytomas and 8 pairs of recurrent oligodendrogliomas by means of interphase in situ hybridization (ISH) to paraffin-embedded, formalin-fixed tissue sections. A set of DNA probes specific for the centromeric regions of chromosomes 1, 7, 10, 17, X and Y was applied. Since LOH studies on oligodendrogliomas have revealed losses in the region of 1p32-1p36, a DNA probe specific for the 1p36.3 locus was included. Hybridization with the 1p36.3 probe revealed loss of 1p in 5 of the 8 oligodendroglioma recurrences, the aberration being present in the primary tumors in 2 cases. In none of the astrocytomas was loss of 1p observed. Numerical aberrations were found in one astrocytoma pair (+7) and in the second biopsy of an oligodendroglioma (+7, -10). Aneuploidy was found by in situ hybridization in 8 of the 13 tumor pairs. Detection of aberrations in the 1p36.3 locus by interphase in situ hybridization to paraffin-embedded, formalin-fixed tumors may become a very useful tool in delineation of oligodendroglial from astrocytic genotypes, directing tumor specific therapy. The technique may be of crucial importance in tumor cases in which histologic criteria of lineage are not obvious.