Scientists have found the first “conclusive evidence” of the existence of cancer stem cells in humans, in a discovery which could put an end to years of scientific controversy and pave the way for more effective cancer treatments which could attack the disease “at the root”.
Researchers at Oxford University and Sweden’s Karolinska Institutet said that their findings were “a vitally important step” in our understanding of how cancers developed and how best to treat them.
The existence of cancer stem cells – mutated stem cells responsible for the development and growth of cancers – has been hypothesised for decades, and their existence in mice was established two years ago. Whether or not they are also responsible for the growth of cancers in humans has remained controversial.
However, in a new study published in the journal Cancer Cell, an researchers said they had tracked gene mutations responsible for a form of blood cancer back to a distinct set of cells which they say are at the root of the cancer’s spread.
The study was carried out in a group of patients with a blood disease which commonly develops into leukaemia, and can only technically prove the existence of cancer stem cells for this particular condition, but the scientists said that “similar” cancer stem cells were likely to lie behind the development of other cancers.
Experts believe the theory of cancer stem cells may be of great importance for future treatments. It suggests that at the root of any cancer are a set of cells responsible for its growth. In theory, if treatments could be developed to specifically target these cells, then a cancer could be eradicated altogether.
“The idea here is that the cancer depends on these stem cells for being able to propagate,” said Dr Petter Woll, of the Weatherall Institute for Molecular Medicine at the University of Oxford. “If we can eliminate the cancer stem cells, it would be like removing a tree by the roots – it won’t grow back, like it would if you removed it by the stem.”
The 15 patients involved in the study had myelodysplastic syndrome (MDS), a blood disorder which causes a drop in the number of healthy blood cells, and develops into acute myeloid leukaemia in around half of all cases.
Researchers investigated malignant cells in the bone marrow of the patients and tracked them over time. Using genetic analysis, they were able to isolate a small and distinct group of MDS cells which were the origin of the cancer-driving DNA changes which were causing the disease to progress.
The researchers emphasised that their findings did not offer any new treatment for MDS or leukaemia patients. However, Dr Woll said that it did give future researchers “a target” for development of more efficient “cancer stem cell-specific” therapies. However, even if cancer stem cells were eliminated, Dr Woll added, there would still be a chance that genetic mutations could lead to other stem cells later becoming cancer stem cells.
Professor Kamil Kranc, a Cancer Research UK stem cell expert based at the University of Edinburgh, said that the findings were a “a huge leap towards understanding the roots of blood cancers”.
“Cancer stem cells have long been thought to be at the heart of many types of cancers but identifying these rogue cells has been a major challenge,” he said. “The next step will be to find specific drugs that eliminate these unique cells, which could be key to helping more people survive cancer.”
Dr Neil Rodrigues, of the European Cancer Stem Cell Research Institute at Cardiff University, said that the new study was “very important”, as it “precisely defines the provenance and biological composition of the cancer stem cell in MDS.”
“The implications for therapy in MDS itself are important as we could now design curative therapies specifically against the cancer stem cell in this otherwise difficult to treat disease and monitor how effective that treatment is,” he said. “If cancer stem cells are definitively identified in human cancers outside the blood system, then this strategy could similarly be applied to effect cure in a wide range of cancers.”
Professor Sten Eirik Jacobsen, also of the Weatherall Institute, who led the study, said that an improved understanding of cancer stem cells could be as crucial as the revolution in our understanding of the genetics of cancer. However, he emphasised that a great deal of work still needed to be done, and cancers which have proven difficult to treat would remain so for the foreseeable future.
“[Cancer stem cells are] a big piece of the puzzle, but only one piece,” he said. “The thing we know about cancers is that many will continue to be very difficult to treat… the big revolution in cancer treatment is that we are learning much more about genetics, that is key, but understanding what are the key cells is also very important.”
Q&A: Cancer stem cells
What are cancer stem cells?
Stem cells are the body's "master cells", which are capable of developing into the various tissues of the body. Mutations in the stem cells – to make "cancer stem cells" have been theorised to be an underlying driver of cancer spread.
How long have we known about them?
The concept of cancer stem cells has been around for many years. A population of leukaemia cells that behaved like cancer stem cells in mice were identified 15 years ago by scientists in Toronto. Further lab experiments made similar findings for other cancers, but many scientists challenged the findings and questions were raised over whether cancer stem cells existed at all. Two years ago definitive evidence of their existence in mice was demonstrated.
What is new about this study?
It is the first which appears to conclusively prove the existence of such cancer stem cells in humans.
How does it change cancer treatment?
At the moment it doesn’t, but it opens up the possibility of more effective cancer therapies which could target the root of the cancer, which experts say could be key to helping more people survive cancer.