Immortality of cancers: a consequence of inherent karyotypic variations and selections for autonomy.

Immortality is a common characteristic of cancers, but its origin and purpose are still unclear. Here we advance a karyotypic theory of immortality based on the theory that carcinogenesis is a form of speciation. Accordingly, cancers are generated from normal cells by random karyotypic rearrangements and selection for cancer-specific reproductive autonomy. Since such rearrangements unbalance long-established mitosis genes, cancer karyotypes vary spontaneously but are stabilized perpetually by clonal selections for autonomy. To test this theory we have analyzed neoplastic clones, presumably immortalized by transfection with overexpressed telomerase or with SV40 tumor virus, for the predicted clonal yet flexible karyotypes. The following results were obtained: (1) All immortal tumorigenic lines from cells transfected with overexpressed telomerase had clonal and flexible karyotypes; (2) Searching for the origin of such karyotypes, we found spontaneously increasing, random aneuploidy in human fibroblasts early after transfection with overexpressed telomerase; (3) Late after transfection, new immortal tumorigenic clones with new clonal and flexible karyotypes were found; (4) Testing immortality of one clone during 848 unselected generations showed the chromosome number was stable, but the copy numbers of 36% of chromosomes drifted ± 1; (5) Independent immortal tumorigenic clones with individual, flexible karyotypes arose after individual latencies; (6) Immortal tumorigenic clones with new flexible karyotypes also arose late from cells of a telomerase-deficient mouse rendered aneuploid by SV40 virus. Because immortality and tumorigenicity: (1) correlated exactly with individual clonal but flexible karyotypes; (2) originated simultaneously with such karyotypes; and (3) arose in the absence of telomerase, we conclude that clonal and flexible karyotypes generate the immortality of cancers.