Facing cancer once is daunting enough, but the shock of relapse often leaves a person feeling overwhelmed and depressed. Now three separate studies seem to confirm scientists’ suspicions that so-called cancer stem cells drive the growth and regrowth of tumors. If true, this changes the whole approach to cancer therapy.
For years, scientists have debated the existence of cancer stem cells, which exhibit stem cell characteristics by producing new tumor cells or additional cancer stem cells. Studies are beginning to show tumors contain a small number of cancer stem cells that are often quiescent, shielding them from chemotherapy treatments that normally target and kill tumor cells.
This means after treatment and enough time, the surviving cancer stem cells divide, producing more cancer stem cells as well as differentiating into the variety of cells found in a tumor. The ability to produce cells with varying characteristics could also help explain metastasis, the migration and adaptation of tumor cells to other organs.
The new studies produced the best evidence yet that cancer stem cells do exist in the tumors of the brain, skin and gut of mice. One group from the University of Texas Southwestern Medical Center in Dallas was able to mark brain tumor (glioblastoma) stem cells using a neuronal stem cell marker. When all the tumor cells were treated with chemotherapy, the only cells that survived were the ones identified by the stem cell marker. When chemotherapy was given along with treatment to repress cancer stem cell activity, the tumors shrank.
Another scientist, Hans Clevers from the Hubrecht Institute in the Netherlands, focused on gut tumor cells. His team found a way to mark cancer stem cells in benign intestinal tumors. They then introduced a gene that would make the cancer stem cells glow green, which gave rise to more green-colored cancer stem cells as well as all the other types cells in that tumor.
To further prove stem cells fuel tumors, Clevers triggered all the stem cells colored green to switch to either yellow, red or blue, and they produced stem cells and tumor cells in that same color.
The third study, led by Belgian scientists, did not specifically label cancer stem cells but labeled individual skin tumor cells so they could be tracked during tumor development. The tumor cells were allowed to reproduce and did so in two ways.
The majority of cells divided a few times then died out. The others continued to grow and divide, supporting the belief that a small subset of tumor cells spurs cancer growth, and these could indeed be cancer stem cells. The more aggressive the tumor cell type, the more likely it was to produce more cells that continue to divide.
These findings provide strong evidence cancer stem cells exist and are the continuous origin of new tumor cells. Scientists have the opportunity to develop therapies that target and kill cancer stem cells and combine these with current, effective chemotherapies that kill tumors cells.