Clonal chromosome abnormalities and in vitro growth characteristics of classical and cellular schwannomas.

Cytogenetic analysis was performed on 12 schwannomas, 10 classical and two of the cellular type. Electron microscopic examination of cultured cells from two classical and two cellular schwannomas revealed features compatible with a Schwann cell differentiation. Immunohistochemical analysis of the cultures demonstrated immunoreactivity for S-100 protein in 6 of 6 cases and for vimentin in 2 of 2 cases of classical schwannoma, thus further supporting the authenticity of the cultured cells. Cultured cells from one cellular schwannoma also exhibited immunoreactivity for glial fibrillary acid protein (GFAP). Cytogenetic analysis of the 12 tumors revealed clonal abnormalities in 10 of the cases. In the majority of tumors, cells with a normal karyotype coexisted with different abnormal clones and sporadic deviations. Numerical changes predominated and were found in all tumors, while structural rearrangements were detected in eight tumors. The most common abnormality was clonal or sporadic loss of chromosome 22, which was found in all cases. Other clonal abnormalities included loss of one sex chromosome found in five cases, -15 found in three cases, and -12, +5, +7, +20 found in two cases each. These results provide further evidence in support of a role for loss of chromosome 22 in the pathogenesis of schwannomas. Our findings also indicate that there exist several different evolutionary pathways for schwannomas, and that some of these are shared by several other types of benign and malignant tumors of the nervous system.