What are adult stem cells?
Every organ and tissue in the body contains a small number of what scientists call adult stem cells or progenitor cells. These cells have three characteristics in common:
1). Adult stem cells can renew themselves through cell division for long periods of time.
2). Adult stem cells retain the ability to give rise to several (but not all) types of cells in the body.
3). Different types of adult stem cells give rise to different specialized cells. Pancreatic stem cells, for example, are the ancestors of insulin-producing islet cells in the pancreas. Hematopoietic stem cells develop into all the different types of cells in the human blood and immune systems.
Cancer stem cells are a type of adult or progenitor cell found in most types of cancer. These cells generally represent just 1% to 3% of all cells in a tumor, but they are the only cells with the ability to regenerate malignant cells and fuel the growth of the cancer.
Is this the same as embryonic stem cells?
No. Embryonic stem cells are primitive cells that form inside an early embryo. These cells also can be generated in a laboratory dish during a process called in-vitro fertilization. Four to five days after a human egg is fertilized by sperm, the dividing mass of cells is called a blastocyst. Scientists can remove the inner cell mass from the blastocyst and grow stem cells in a culture dish in the laboratory. Under the right conditions, these stem cells will retain the ability to divide and make copies of themselves indefinitely. Unlike adult stem cells, embryonic stem cells have the ability to give rise to any of the more than 200 different types of cells in the human body.
Why is research on cancer stem cells important?
Cancer research focuses on stem cells present in malignant tumors. Researchers believe current cancer treatments sometimes fail because they don't destroy the cancer stem cells. Think of cancer as a weed: the stem cells are the root while the remaining majority of the cells are the part of the weed above ground. If you remove only the leaves but not the root, the weed will grow back. The same is true for cancer: if you do not kill the cancer stem cells, the cancer is likely to return.
Recent reports show cancer deaths are decreasing, so aren't we doing a good job already of killing cancer?
In some cancer types, we are doing a good job. Most cancers when caught early can be successfully treated. But doctors still struggle to treat advanced cancers and some cancer types, such as pancreatic cancer, still have incredibly dismal survival rates. Other cancers, such as head and neck cancers, are often resistant to current therapies, making less-invasive treatments more difficult. In addition, current chemotherapies cause severe side effects because they target all rapidly dividing cells. Treatments that target only cancer stem cells would cause fewer side effects for patients.
In what tumor types have cancer stem cells been identified?
Cancer stem cells were first identified in leukemia. U-M researchers discovered the first cancer stem cells in solid tumors, finding them in breast cancer. Since then, cancer stem cells have been identified in brain, colon, head and neck, pancreas and central nervous system tumors. Work is ongoing to identify stem cells in other tumor types.
How are cancer stem cells identified?
Researchers take samples of tumors removed from patients during surgery, always with the patient's informed consent. The cells within the tumor are then sorted based on their expression of certain cell markers on their surface. Sorted cells can be injected into mice, which are then watched for new tumor growth. When only specific sorted cells form new tumors, researchers then test those cells for properties of stem cells.
What happens after stem cells are identified?
The next step is to understand how cancer stem cells work and identify drugs that will kill the stem cells without harming normal cells.
What research is the University of Michigan doing in cancer stem cells?
Cancer Center scientists are working on cancer stem cells in virtually every tumor type. In 2003, U-M researchers reported on the first discovery of cancer stem cells in a solid tumor type, which was in breast cancer. Since then, U-M researchers have also been first to identify pancreatic cancer stem cells and head and neck cancer stem cells.
In 2006, investigators at the Cancer Center began the first phase I/II clinical trial targeting breast cancer stem cells. The experimental drug being tested in this study was shown to target cancer stem cells in laboratory animals.
Research is ongoing to look at whether Bexxar, a treatment developed at U-M for lymphoma, attacks cancer stem cells in multiple myeloma, a type of blood cancer.
Scientists throughout the Cancer Center are conducting research on cancer stem cells to understand the genes, proteins and signaling pathways these cells use to trigger and drive the development of cancer.
For a more complete overview of the U-M Cancer Center's cancer stem cell research, please read Cancer's Stem Cell Revolution.
Are clinical treatments available now to target cancer stem cells?
The work on cancer stem cells is still in early stages, primarily taking place in the laboratory and early clinical trials. U-M is conducting clinical trials of experimental therapies targeted at cancer stem cells in multiple myeloma, pancreatic cancer and breast cancer. Initial results are positive, but additional trials in a larger number of patients will be necessary. If these new drugs are proven to be safe and effective, they could become the first approved cancer treatments to be developed as a result of cancer stem cell research. Visit UMClinicalStudies.org to see what clinical research opportunities are currently available.