SHARED ALLELIC LOSSES ON CHROMOSOMES 1P AND 19Q SUGGEST A COMMON ORIGIN OF OLIGODENDROGLIOMA AND OLIGOASTROCYTOMA

Loss of heterozygosity (LOH) in specific chromosomal regions, which ar e likely to harbor tumor suppressor genes, has been associated with hu man gliomas. In this study we have analyzed astrocytic and oligodendro glial tumors for LOH on chromosomes 1 and 19. By microsatellite analys is LOH was found on chromosome arm 1p in 6/15 oligodendrogliomas WHO g rade II and III, 12/25 oligoastrocytomas WHO grade II and III, 6/79 gl ioblastomas WHO grade IV, 5/44 astrocytomas WHO grade II and III and 0 /23 pilocytic astrocytomas WHO grade I. The high incidence of LOH on c hromosome arm 1p in oligodendrogliomas and oligoastrocytomas indicates that a putative tumor suppressor gene in this region is involved in t he formation of gliomas with oligodendroglial features. Furthermore, t he frequent involvement of chromosome arm Ip in oligodendrogliomas and oligoastrocytomas, but not in astrocytomas, suggests that genetically oligoastrocytoma is more similar to oligodendroglioma than to astrocy toma. In order to support this hypothesis, oligodendroglial and astroc ytic areas in three mixed oligoastrocytomas were examined differential ly for LOH 1p and for LOH 19q, the second genetic region believed to b e affected in these tumors. All three tumors had LOH of 1p and LOH of 19q in both areas of oligodendroglial and of astrocytic differentiatio n. These findings show that the astrocytic and oligodendroglial portio ns of oligoastrocytoma share molecular genetic features and probably a re of monoclonal origin.