The accumulation and occurrence of clonal and unstable rearrangements are independent in colorectal cancer cells.

The rates of unstable and clonal rearrangements were compared in a series of colorectal cancers. These tumors were classified in relation to their karyotypes, into monosomic (MT), trisomic (TT), or normal (NT) type. MT have multiple, TT have few, and NT have no clonal, generally unbalanced, chromosome rearrangements. The rates of unstable rearrangements, i.e. chromatid and chromosome breaks, chromatid exchanges, dicentrics, and telomeric associations, were found to be very similar in these tumors, suggesting identical chromosome instability defined as the occurrence of nontransmissible rearrangements at each cell generation. Thus, the chromosomal patterns of these tumors seem to be rather driven by the specific selection of chromosome alterations than by differential rates of occurrence of rearrangements.