Ring chromosome 12 resulting from nonrandom telomeric associations with the short arm of chromosome 15 in a cerebellar astrocytoma.

Ring chromosome 12 was found in an untreated cerebellar astrocytoma apparently resulting from nonrandom telomeric associations involving the short arm of chromosome 15, and both the long and short arms of chromosome 12. The clonal nonrandom telomeric associations of 15p to both ends of the chromosome 12 were transitory, but appear to be the precursor lesion in the evolution to ring chromosome 12 in this tumor. A multistep process in the formation of a ring chromosome resulting from nonrandom telomeric associations to both telomeres is illustrated.