The karyotypes of 18 primary 'untreated' gliomas, 6 recurrent gliomas
treated with radiotherapy and/or chemotherapy and 2 gliomas before and
after treatment are described, based on observations using standard c
ytogenetic techniques. In comparison to the untreated gliomas there we
re relatively consistent chromosome differences in the treated gliomas
, including (1) deletions of the long arm of chromosome 7 with breakpo
int at q22, possibly induced by alkylating agents, and (2) numerous si
ngle cell abnormalities or unrelated clones of structural abnormalitie
s, presumably induced by radiotherapy.