Spontaneous, malignant transformation of hamster embryo cells in vitro

Primary hamster-embryo cells were dispersed in vitro. The frequency of colony development depended on the original method used for dispersing the cells and on the number of cells seeded. Cell populations derived from passages in vitro of 3 colony isolates produced tumors when inoculated into baby or adult hamsters. Similar populations derived from primary or confluent, passaged cell cultures failed to produce tumors. The transformed cells were long, parallel fibroblasts or short, randomly arranged spindle types. It is suggested that malignant, spontaneous transformation of cells occurs within a limited number of passages in vitro and that these cells may be a factor in virus-induced cell transformations.