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.
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.
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.
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.
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.
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.
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