Hypermutability in carcinogenesis.

The presence of numerous chromosomal changes and point mutations in tumors is well established. At least some of these changes play a role in the development of the tumors. It has been suggested that the number of these genetic changes requires that tumorigenesis involves an increase in mutation rate. However, the presence of numerous changes can also be accounted for by efficient selection. What is required to settle the issue is some measure of nonselected mutations in tumors. In order to determine whether the tumor suppressor TP53 (coding for the protein p53) is hypermutable at some stage of carcinogenesis, the frequency of silent and multiple mutations in this gene has been examined. Silent mutations make up approximately 3% of the total recorded but constitute 9.5% of the mutations found in tumors with multiple mutations. Multiple closely linked mutations are also observed. Such multiple mutations suggest the operation of an error-prone replication process in a subclass of cells. The published data indicate that TP53 is hypermutable at some stage of tumor development. It is not yet clear whether TP53 is unique or whether other genes display a similar pattern of silent and multiple mutations.