Thursday August 2 2012
Cancerous stem cells may trigger the return of some cancers
“Cancer cell discovery could revolutionise treatment,” said The Independent today. These reports are based on an American study looking at brain cancer in mice.
The mice in this study had been genetically engineered to have a highly aggressive form of brain cancer. The cancer often returns after chemotherapy in humans, and has an average survival period of just a year after diagnosis.
The scientists who ran the study wanted to see if they could identify a specific group of cancer “stem cells” that might be responsible for the return of the cancer.
Stem cells are remarkable cells that can transform into virtually any other cell type found in the body – a sort of biological blank canvas.
The mice were treated with a cancer drug, and the scientists identified a subset of tumour cells that seemed to be responsible for the tumour regrowing after treatment. These tumour cells seem to behave in much the same way as adult stem cells.
The results are also supported by recently published research that found a similar association with stem cells and the regrowth of some types of skin cancer and digestive system cancer.
This avenue of research is potentially very exciting as there may be a way to kill these cancerous stem cells. If so, then new treatments may become available for types of cancer that have previously proven resistant to conventional treatment.
But any excitement has to be tempered with realism. It could take many years of research in this field to find out if similar cancer stem cells exist in humans and, if so, how and if they can be treated.
Where did the story come from?
The study was carried out by researchers from the University of Texas and was funded by various academic grants including one from the National Institutes of Health. It was published in the peer-reviewed) scientific journal Nature.
The research was explained clearly in the media, making it accessible to the public. However, there was too much emphasis on the possibility that these finding would lead to “new ways of fighting cancer” as The Daily Telegraph put it. While this is possible, the research has only been conducted in mice and, also, only on certain types of cancer. The study identified a type of cell that may be responsible for the growth of a particular type of brain cancer in mice, but, as yet, ways to target this type of cell to treat the cancer have not been developed.
What kind of research was this?
This was an animal study that looked at the development in genetically engineered mice of a type of brain cancer called glioblastoma. This is the most common type of malignant brain tumour in humans. It is very aggressive and often returns after surgical removal. The researchers say that it is not known how the cancer comes back. Their hypothesis is that adult nerve system stem cells are the probable source of this recurrence and they used genetic techniques to investigate this.
Stem cells are cells that have the capacity to develop into different specialised cell types. The main role of adult stem cells is to repair and maintain the tissue in which they are found.
What did the research involve?
The researchers used mice that had been genetically engineered to develop a type of brain tumour called gliomas, which includes glioblastoma. Once the mice had developed tumours they were treated with the chemotherapy drug temozolomide (TMZ), which is currently used to treat glioblastoma in humans. The researchers did this to temporarily stop the tumours growing. They then used various methods to look at what types of cells started the regrowth of these tumours.
They tested whether killing off these cells could stop the tumours growing in the first place or could prevent them from regrowing after chemotherapy. A control group of mice received no treatment to kill these cells. The treatment used to kill the cells could only do this because the mice were genetically engineered to allow it to work. The treatment used would not kill these cells in a normal mouse or human.
What were the basic results?
The researchers identified a “subset” of tumour cells that seemed to be largely responsible for the regrowth of tumours in the mice genetically engineered to develop gliomas and treated with TMZ. These cells seemed to behave similarly to adult nerve system stem cells. They did not normally divide very much in the tumour but once the actively dividing cells in the tumour had been killed off by TMZ, they started dividing and this allowed the tumour to grow again.
If the genetically engineered mice were treated to kill these cells just as the brain cancer cells started to develop, these mice had much less developed brain tumours than the untreated mice, and lived longer than the untreated mice. Giving the treated mice the chemotherapy drug TMZ as well further reduced growth of the tumours.
How did the researchers interpret the results?
They researchers say that while previous studies have only been able to look at the possible existence of cancer stem cells in tissue in an artificial environment, their study directly identifies a possible glioma stem cell within a living organism. This cell type seems to allow initial tumour growth and tumour regrowth after chemotherapy.
They say that further evaluation of these cells and their properties is needed and could yield important insights into “novel therapeutic targets” for brain tumours.
This animal study in a mouse model of brain tumour is likely to be of great interest to cancer researchers. The authors note that these are only “putative” cancer stem cells – which means that the results are not yet fully proven, and more research is needed.
As with all laboratory animal research there may be differences in terms of cancer development in humans, but this type of study would not be feasible in humans. Researchers will also want to determine whether there are similar types of cells in other types of cancer. In fact, the news today also reports on two other studies that have found similar types of cells in skin cancers and digestive system cancers in mice.
Reports that this experiment could “revolutionise” cancer treatment are premature. If further experiments suggest that these cells are responsible for the growth of these brain tumours, research will be needed to develop a way to kill them off. The treatment used to kill the cells in this study could only do so because the mice were specially genetically engineered to allow it to work. The treatment used would not kill these cells in a normal mouse or human.
This further research will take time and, unfortunately, is not guaranteed to result in a successful new form of treatment for humans. However, the study provides useful additional information on how this difficult-to-treat form of brain cancer may grow and evade the effects of chemotherapy.
Analysis by NHS Choices. Follow Behind the Headlines on twitter.