[Data are presented that] are consistent with the linear progression model when it is assumed that there are two types of cells in tumours: those that can initiate metastases (metastasis-forming cells (MFCs)), which probably derive from tumour stem cells[ref 7] and those that probably cannot initiate metastasis because their proliferative ability is limited[refs 7,8,9].Response to the commentary: Tumour cell dissemination and growth of metastasis by Christoph A Klein, Nat Rev Cancer 2010(Feb); 10(2): 156. Excerpt from the full text of the response:
Finally, the authors declare that the parallel progression model is incompatible with the cancer stem cell hypothesis. As defined above, parallel progression does not address this issue.The 'linear progression model' described by Christoph Klein "places major evolutionary events in the primary tumour and late dissemination of fully malignant cells that subsequently grow to manifest metastases". In the 'parallel progression model', there is "early dissemination of tumour cells from the primary tumour and ectopic selective adaptation (which is associated with the emergence of genomes fully able to form metastases)" (see Christoph Klein's response).