Transformed cells are created by exposing embryo cells (or fibroblasts) to ionising radiation or chemicals. When viewed on a plate, the transformed cells will tend to pile up with haphazard cell-cell orientation.
The other types of transformed cells are from immortal cell lines which originated from mouse embryos.
Malignant cells tend to behave in a similar way to transformed cells in vitro. Alternatively, they may be grown as spheroids in a stirred suspension. The spheroid mimics the characteristics of solid tumours, with the central, more hypoxic core at a distance from any drugs or radiation that may be used to treat the tumour.
Spheroids typically lack the connective tissue and vasculature seen in in vivo malignancies thereby not creating a fully accurate model of tumour behaviour.