The malignant stem cell.

A recent study of embryonic cells at organogenesis revealed that their nucleus was bare of cytoplasm along one section of the envelope, and that they formed aggregates in which nucleus to nucleus contact was a feature. Their behaviour could be divided into three stages, the first when the embryonic cell was small and motile, the second when cell aggregation took place and the third when differentiation occurred. The embryonic cell at organogenesis was considered to be committed and hence stem cell in nature. It is hypothesized that stem cells in the adult also start off as small, motile embryonic-like cells and progress through the same three stages. This embryonic-like structure and behaviour also applies to the malignant stem cell, and evidence is put forward to support this view. Finally the suggestion is made that metastases are due to the small size and motile nature of the malignant stem cell, and not due to a decrease in any adhesive forces between tumour cells.