However, trials in unselected patient populations in solid tumours have been generally disappointing, highlighting the need for predictive biomarkers to stratify responsive patient populations and identification of rational clinical combinations of these agents with other drugs based on pre-clinical research.
Results from experiments using primary human cancer tissue have shown that not all cells in a tumour are equivalent; a minority tumourigenic cell population exists in solid tumours of both the breast and the brain which represents around 1% to 2% of the total tumour burden [ 35, 42].
The activated Notch signals can inhibit hematopoietic stem cell differentiation and maintain their pluripotency [ 36, 37], and maintaining the stem cell population in several solid tissue types, including several neuroectodermal tissues [ 38].
Between 1 and 5percentt of the world's urban population is employed in solid waste management, meaning anything to do with the collection and disposal of waste, according to a recent report from the World Bank (h/t the Washington Post ).
Several studies suggest the presence of a rare population of cells in solid tumors and leukemia that possess the capability to regenerate and propagate the tumor [19], [20], [21], [22], [23].
Taken together, CD133/AC133 is an indicator, but definitely not a reliable marker for defining a population of CSCs in solid tumors since it does not characterize tumor-initiating cells exclusively.
FCM on fine-needle tumour aspirates was used to determine the relative proportions of the cell populations in mixed solid tumours in which E1.95 showed a growth-dominating effect on E1.15.
Since then, resistance to chemotherapy and/or radiotherapy has been linked to CSC sub-populations in various solid tumours, including glioblastoma (Bao et al, 2006; Liu et al, 2006; Salmaggi et al, 2006), breast (Phillips et al, 2006), lung (Eramo et al, 2008) and colon (Todaro et al, 2007) cancers.
In the meantime, strong evidence suggests the existence of this rare and highly tumorigenic CSC population in several major solid cancers, including brain, colon, and breast carcinomas.
Increasing evidence suggests that MSCs might be a suitable cell population for immunosuppressive therapy in solid organ transplantation and may be strong candidates for cell therapy against human autoimmune diseases [ 70- 72].
