Cancer stem cells (CSCs) are a type of cancer cell that have the ability to give rise to all the cell types within a tumour. CSCs are thought to form the 'root' of the cancer and are responsible for driving its growth and evolution. Their existence, however, has been debated for decades by the scientific community, as clear evidence of their appearance in human cancers has so far been lacking.
'We have identified a subset of cancer cells [and] shown that these rare cells are invariably the cells in which the cancer originates', said study author Dr Petter Woll, from the University of Oxford. 'It suggests that if you want to cure patients, you would need to target and remove these cells at the root of the cancer'.
Scientists investigated 15 patients with myelodysplastic syndromes, where the bone marrow does not make enough healthy blood cells. Over time, MDS can develop into a form of leukaemia called acute myeloid leukaemia (AML) through an accumulation of specific genetic mutations.
The researchers took samples of the patients' bone marrow at several points during the progression of the disease and identified cancerous cells. By analysing genetic changes, they were able to track the origin of mutations leading to cancer cell formation. They found a subset of MDS cells that showed the distinctive markers of stem cells, which they identified as CSCs as they were the only cell type that was able to fully reproduce a tumour, supporting the theory that they function as 'roots'.
Current cancer treatments, like chemotherapy, aim to reduce the overall size of the tumour. Chemotherapy attacks the cells that form the bulk of the tumour, but might not reach the smaller population of CSCs, which could then regenerate the tumour and cause a relapse of the disease.
'It's like having dandelions in your lawn. You can pull out as many as you want, but if you don't get the roots they'll come back,' explained Dr Woll.
CSCs have been found in a number of human cancers to date, but the findings have remained controversial as the lab tests used in their identification were thought to be unreliable.
'In our studies, we avoided the problem of unreliable lab tests by tracking the origin and development of cancer-driving mutations in MDS patients', said study lead Professor Jacobsen.
The results are promising but should be interpreted with caution as these results are limited to the MDS and might not be applicable to other forms of cancer. Dr Woll noted: 'We can't offer patients today new treatments with this knowledge. What it does is give us a target for the development of more efficient and cancer stem cell specific therapies to eliminate the cancer'.