In the molecular biology of the cell (6th ed), it is stated that:
Some cancers seem to be organized in a similar way: they consist of rare cancer stem cells capable of dividing indefinitly, toghether with much lager numbers of dividing transit amplifying cells that are derived from the ancer stem cells but haave a limited capacity for self-renewal. These non-stem cells appear to constitute the great majority of the cell population of some tumorus (p.1121).
Although in an earlier segment, however, we can read that:
Human cancer cells avoid replicative cell senescense in one of two ways. They can maintain the activity of telomerase as they proliferate, so that their telomeres do not shorten or become uncapped, or they can evolve an alternate mechamism based on homologous recombination (called ALT) for elongating their chromosome ends. Regardless of strategy usedd, the result is that the cancer cells continue to proliferate under conditions when normal cells would stop (p.1100).
How do we interpret these two passages? Are some cancer cells incapable of lenghtening their telomeres, and is it these types of tumours that can't persist without cancer stem cells? Or are cancer stem cells beneficial in some other way to the tumour (such that a tumour stem cell might differentiate into several types of tumour cells, which might be suitable for different environments)?
I understand that having cancer stem cells that proliferate at a slower pace than regular cancer cells might be beneficial for withstanding things like chemotherapy. But what's being emphaphized is not their capacity for survival, but their greater ability at self renewal?