The discovery could provide a new source of cancer stem cells that scientists will be able study to investigate the role of stem cells in tumour growth. The artificial stem cells could also act as targets for potential cancer drugs. Cancer stem cells live within a tumour, and it is thought that they self-renew and maintain the tumour growth. Future cancer drugs will need to target both cancer stem cells as well as the tumour cells themselves, and the new artificial cancer stem cells could be used to test potential drugs. The artificial stem cells could also provide insight into how the cancer stem cells develop in a tumour a the first place. "By the time a patient comes to a hospital, they already have a cancer, so that process has already happened," said Howard Chang, who is also a member of the Stanford Cancer Center. The new work may present ways of preventing this process at an early stage of cancer development. Previously, scientists had to take the stem cells from cancer patients to study them directly, but the new research would provide a new, more readily available, source. "Studying cancer stem cells has been challenging because these cells are rare sub-populations within the tumour and are difficult to purify," explains David Wong, lead author of the paper, published in the journal Cell Stem Cell. "The ability to experimentally create cancer stem cells offers a new resource to investigate the mechanism by which cancer stem cells arise from normal cells." The researchers began to investigate the origin of cancer stem cells by comparing the genetic activity in embryonic stem cells with cells active in normal adult stem cells, to find that the embryonic stem cells contained a large number of genes that were dormant in the adult stem cells. They then compared these results with the genetic activity of the cancer stem cells. Somewhat surprisingly, they found that this genetic activity resembled the activity in embryonic stem cells. Previously, scientists had thought that these genes were permanently silenced after birth, but the research shows that cancer stem cells must somehow turn them on again. The group also noticed that the genes active in both embryonic and cancer stem cells are controlled by a few biological master regulators. One of those genes, called Myc, has also been shown recently to help convert normal skin cells into embryonic-like cells. By activating two genes in addition to Myc in normal skin cells, those cells were transformed into what appeared to be cancer stem cells. According to Wong, when the team transplanted the cells into laboratory mice, as few as 500 stem cells caused a 150-fold increase in the size of the tumour.