Genotypic and phenotypic changes of a mouse lymphoma during long-term cultivation.

NK/Ly mouse lymphoma ascites cells were explanted and established in culture. The cells grew in monolayer and showed fibroblast-like morphology. The original NK/Ly cells contained one large metacentric marker chromosome, while the in vitro growing cells had two metacentrics in the early passages. These so-called bi-armed chromosomes were growing in number, up to seven, along with the number of subcultures. No tumour "take" was observed when the cells were given into mice intraperitoneally. However, a solid tumour developed following injection of cells into the leg muscle. The histological picture of this solid tumour was anaplastic sarcoma. It is concluded that the accumulation of bi-armed chromosomes, which were formed either by anaphase bridges, or by centric fusion of telocentric chromosomes, led to a profound alteration of lymphoma resulting a phenotype of anaplastic sarcoma.