Spontaneous in vitro neoplastic evolution: recurrent chromosome changes of newly immortalized Chinese hamster cells.

Spontaneous neoplastic progression in cultured Chinese hamster cells was studied at the earliest stage possible. Eighteen independent newly immortalized cell populations (from six individual Chinese hamsters) were characterized for karyotype instability. Colonies were selected from initial sparse platings of adult or fetal cells and were expanded for study. The chromosomes from these newly established cell lines were studied using a combination of G-banding and flow karyotype analysis. At a slightly later passage, the 18 cell lines were tested for tumorigenicity in nude mice. Frequent recurring chromosome changes were observed in the karyotypes. The most frequent changes were either total or partial trisomy of chromosome #3 (83%) and trisomy of chromosome #5 (61%). Only 4 of 18 clones (22%) were tumorigenic at the time of testing, and these had long latent periods. The presence of recurrent chromosome changes did not obligate these cell lines to become tumorigenic, but the karyotype instability appeared to be an indicator of the ongoing process of neoplasia.