When Ehrlich ascites cells were fused with diploid fibroblasts, isolated directly from the animal, the resulting hybrid cells regularly produced progressive tumours. However, an analysis of a range of clonal populations of these hybrid cells, each derived from a separate primary fusion, revealed that the chromosomal constitution of these cells was highly unstable; all cell populations were found to have already undergone substantial chromosome losses by the time enough cells were available to permit chromosomal analysis. Thus, although these hybrid cells were highly tumorigenic, the tumours arising from them were not composed of cells with complete parental chromosome sets, but of cells from which some chromosomes had been eliminated.

Fellow of the International Agency for Research on Cancer, on leave from the Institute of Oncology, Warsaw, Poland.