Cancer stem cells
The idea of cancer stem cells has slowly increased in credibility over the last ten years. The leukaemia stem cell was the first such cell to be described but it has been suggested that cancers of the brain, colon, ovary, pancreas, and prostate may also have stem cells. The origins of these cells are controversial. The concept is based on the notion that, as with normal stem cells, a pool of malignant cells has the ability to indefinitely self renew and re-initiate tumours in distant locations. As with normal stem cells, these cells only divide slowly (in other words self renew), which makes them more resistant to anti-cancer drugs that usually kill rapidly dividing cells, while their differentiated daughter cells remain sensitive. One explanation of leukaemia stem cells is that the genetic damage leading to cancer takes place in a newly differentiated cell followed by a de-differentiation event triggered by the stem cell niche, resulting in a very limited but immortal supply of leukaemic stem cells. In solid tumours it is extremely difficult to pinpoint the precise origin of the putative cancer stem cell as the tumour has a heterogeneous population of mutant cells. Among these cells there may be several types of stem cells, one optimal to the specific environment and several less successful lines. The latter cells can become more successful in some environments, allowing the tumour to further adapt to changes in its environment. Ongoing stem cell research may have repercussions on new cancer treatment.