Identification of a ring chromosome in a myxoid malignant fibrous histiocytoma with chromosome microdissection and fluorescence in situ hybridization.

We investigated the origin of a ring chromosome in a myxoid malignant fibrous histiocytoma (MFH) by microdissection and fluorescence in situ hybridization (FISH) analyses. Cytogenetically, only two ring chromosomes were observed; the smaller ring was seen more frequently. The latter was microdissected, and the material used for FISH. Hybridization of the microdissected labeled DNA to normal metaphase cells revealed that the signal localized only to 20q. Three signals were seen in the tumor cells using either the microdissected 20q probe or chromosome 20 centromeric probe, indicating the involvement of both the long arm and the centromere in the ring chromosome. The short arm of chromosome 20 did not appear to be involved in the formation of the ring chromosome.