Many chemicals, known as complete carcinogens, can both initiate and promote a tumour; others, called incomplete carcinogens, are capable only of initiation.
Studies in xenograft models have shown that multiple subclones capable of leukemia initiation arise in parallel, and that most of the clones that initially form a tumor do not survive long term and do not have the capacity for self-renewal because they disappeared upon retransplantation [3].
Recent data from both hematologic malignancies and solid tumors have suggested that there are only minor populations of cells in each malignancy that are capable of tumor initiation which are the cancer stem cells (CSC) [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15].
Implantation of as few as 100 ALDH+ cells was capable of tumour initiation (Huang et al, 2009).
Consequently, only the NCAM+ALDH1+ were capable of tumour initiation suggestive of their in vivo self-renewal capacity (Table 4).
Cancer stem cells (CSCs) are an important subpopulation of tumor cells which are capable of tumor initiation and are resistant to chemotherapy [ 11].
This subset of human CD133+ fetal brain cells is capable of neurosphere initiation, self-renewal, and multilineage differentiation at the single-cell level [ 20].
Recent data from both hematologic malignancies and solid tumors have suggested that there are only minor populations of cells in each malignancy that are capable of tumor initiation.
This subgroup of cells has also been shown to be more capable of tumour initiation in subcutaneous models (Hirschmann-Jax et al, 2004; Loebinger et al, 2008b).
