Tumour stem cells: the biological concept and its application in cancer treatment.

Experiments in different transplantable mouse tumours suggest that a proportion ranging from 0.1% to 100% of all tumour cells in these different tumours meet the functional definition criteria of tumour stem cells, i.e. regrowth of the tumour proceeded by clonal expansion from a single cell with unlimited proliferative potential. It is concluded that the proliferative organization of many or most human tumours may resemble that of the tissue of origin with a small proportion of stem cells and the majority of transit cells, both proliferating or resting. Cell loss and accelerated repopulation are due to regulated changes in the symmetry constraint of stem cell divisions.