Ring chromosomes in human neoplasias

Though reported from a wide variety of human neoplasias, ring chromosomes, in general, are a rare finding in these diseases. The majority were detected by chance when tumors were screened for chromosomal aberrations. In most cases they are a part of highly complex karyotypic alterations and therefore part of unfavourable prognostic factors. However, in some tumor entities (e.g. tumors of mesenchymal origin) they are of such high prevalence (up to 70% of these tumors) and of such extraordinary specificity that they can even serve as cytogenetic hallmarks for differential diagnosis and for prognostic purposes. The well-known technical problems in malignant cells of achieving high banding quality to define all single chromosomal alterations have severely hampered clear identification of the chromosomes involved in rings until recently. Substantial progress of ring identification could only be achieved when molecular cytogenetic techniques became available. By these techniques it could not only be shown that certain breakpoint regions nonrandomly contribute to ring rearrangements which--at least in certain malignancies--are of basic importance, but also the molecular consequences of these changes could be defined in some cases. The present review summarizes a great number of reports on a total of 760 ring chromosomes in human neoplasias at different sites, but includes only cases with clearly identified rings. In addition, the molecular consequences of ring formation are addressed wherever pertinent information has recently been presented in the literature.