Three research groups, each studying a different type of cancer in mice, have published results that support the theory that tumour growth is driven by cancer stem cells.
The cancer stem cell theory asserts that a small subset of cells within a tumour behave like stem cells, dividing and differentiating to produce all the cells making up the tissue - or in this case, the tumour. Crucially these cancer stem cells are resistant to conventional chemotherapy and radiotherapy treatments and are thought to restart growth of new tumours after treatment, leading to recurrence of the cancer.
Previous work has shown that certain subsets of cells that make up a cancerous tumour were able to grow into new tumours when transplanted in mice, leading to the suggestion of a cancer stem cell. However there was concern that removal of cells from their natural environment during the transplant may alter their behaviour.
In the latest research, scientists used techniques to label or mark cancer cells, allowing them to determine the origin of tumour cells in the same host mammal. The results, published in Nature and Science, provide further evidence of cancer stem cells in brain, skin and intestinal cancers in mice.
One group studied a highly aggressive form of brain cancer, glioblastoma, in genetically engineering mice. Patients with the condition commonly suffer recurrence following chemotherapy, with an average survival rate of just one year after diagnosis. The mice were treated with a chemotherapy drug, killing the majority of the tumour cells, but a small subset of labelled cells persisted after treatment. The treated mice went on to redevelop tumours, with the new tumour cells all deriving from the original labelled cells. However, when these labelled cells were genetically suppressed (in conjunction with the chemotherapy treatment) the mice did not suffer a similar recurrence.
'We've identified the true enemy', said Professor Luis Parada from the University of Texas Southwestern Medical Center in Dallas, who led the brain study. 'There is going to be a paradigm shift in the way that chemotherapy efficacy is evaluated and how therapeutics are developed', he added. A key test of effectiveness is now whether potential treatments can target the cancer stem cells, opposed to simply shrinking a tumour.
Other scientists have also reacted positively to the new research. Robert Weinberg, professor of biology at the Whitehead Institute in Cambridge, Massachusetts said: 'They have made a major contribution to validating the concept of cancer stem cells'.
All three groups say the next step is finding out how these labelled cells relate to putative cancer stem cells previously identified in transplantation studies. Researchers are already searching for ways to target and kill these cells, and these new studies may aid this.