About a decade ago, Max Wicha, a physician at the University of Michigan Comprehensive Cancer Center, hypothesized that stem cells the cells inside the body that have the potential to develop into many different cell types played a role in tumor growth.
He was so confident in his belief that he told the Philadelphia Inquirer in 2005 that he expected a huge explosion in cancer stem cell research “within the next five years. Many of his colleagues were skeptical. But findings from three research letters recently published in Nature suggest that that are indeed a group of cells inside a tumor that act like stem cells.
I know that when most of us think about stem cells, we think about the stem cell research that is exploring the potential for using these cells to treat diseases, conditions or disabilities. But cancer researchers have been studying stem cells for a different reason: They think there might be certain cancer cells inside a tumor that have the same unique abilities as or might even be stem cells.
If this all sounds a bit confusing, think of it like this: Imagine that a tumor is like a beehive. The stem cells are the queen bees that hide in the hive, are hard to kill, and who all the other bees are working to please. As long as the queen exists there is potential for a hive. All the other cancer cells are like worker bees. They do the tumors work of growing, dividing, and spreading, but they are unable to go off on their own to start a new hive (tumor).
The research letters in Nature describe laboratory studies conducted by three different research teams that investigated cancer cells taken from the brain, the intestine, and the skin. The research group studying squamous skin cancers used a genetic labeling strategy that allows individual tumor cells to be tagged and then traced over time as a tumor develops. This study, which was done in mice, showed that tumor tissue like normal tissue contains two types of cells: the queen bee stem-cell like cells and regular cancer cells.
The studies conducted on intestinal tumors also showed that early cancers contain both the cancer stem cells and the other cells. And the research group studying brain tumors in mice found that combining a standard chemotherapy drug with selective killing of the cancer stem cells reduced tumor size almost twice as much as the standard chemotherapy alone.
What do these studies mean for cancer research? For the first time we now have evidence that every cell inside a cancer cell is not equal. There are queen bee-like stem cells and worker bee-like cells, and each type of cells plays a different role in cancer development. They also all don’t respond to chemotherapy in the same way.
These studies are also an excellent example of how cancer research moves from a hypothesis to testable ideas and then, based on that research, more testable ideas. Now, these researchers and others will be asking more questions like: Do all tumors have two types of cancer cells? What happens when therapies are targeted at the cancer stem cells? Would a worker bee cell transform into a queen bee if we had therapies that targeted only the cancer stem cells? Can we change the microenvironment in ways that would keep the cancer stem cells in check? There is so much we now need to know.
It will be some time before we have answers and these answers will undoubtedly lead to more questions. But this is clearly one of the roads we must travel if we hope to finally understand how cancer starts and how to prevent it.