Cytogenetics and cancer.

When present, chromosome abnormalities can contribute useful information for tumor diagnosis and prognosis. However, the existence of diploid tumor cells indicates that such abnormalities are not necessary in tumors. Their time of appearance, sometimes preceding or predisposing to tumor and sometimes occurring late in disease, also suggests that chromosomal events are not critical. Rather, they should be considered as markers of the underlying and essential gene changes. The great frequency of chromosome aberrations in human tumors probably reflects two roles: (1) they provide an efficient means to effect a multiplicity of gene changes, and (2) they permit rapid cellular evolution.