A preneoplastic stage in the spontaneous neoplastic transformation of syrian hamster embryo cells in culture.

Spontaneous neoplastic transformation of Syrian hamster embryo cells in culture occurs in at least two steps. An intermediate stage is represented by an aneuploid cell line which is preneoplastic. These cells differ from the diploid cells by a number of properties, including their ability to become neoplastic in vivo when injected while attached to a substrate. These results support a multistep process for neoplastic transformation of cells in vitro and caution against considering aneuploid cell lines as "normal" cells.