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Cancer Stem Cells Frequently Asked Questions (FAQ)

What are cancer stem cells?

Cancer stem cells are the small number of cells within a tumor that are capable of fueling the tumor's growth. These cells generally represent fewer than 5 percent of all cells in a tumor.

Stem cells have three characteristics:

Is this the same as embryonic stem cells?

No. Embryonic stem cells are primitive cells that can be generated in a laboratory dish. Four to five days after an egg is fertilized by sperm in a dish as part of in-vitro fertilization, 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. Scientists are beginning to understand how to make these cells develop into any of the more than 200 different types of cells in the human body. Cancer stem cells are a different type of stem cell with unregulated growth.

Why is it important to identify cancer stem cells?

Cancer research is focused on adult stem cells present in malignant tumors. These are referred to as cancer stem cells.

Researchers believe current cancer treatments sometimes fail because they are not attacking 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 believed of cancer: if you do not kill the cancer stem cells, the cancer will 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 found?

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?

U-M researchers 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. A clinical trial is currently underway 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. In addition, researchers hope to soon begin a Phase I clinical trial testing a drug that would target breast cancer stem cells.

For a more complete overview of the U-M Cancer Center's cancer stem cell research, please read Cancer's Stem Cell Revolution.

Are 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. U-M is conducting a clinical trial of a possible target for multiple myeloma stem cells and hopes to soon begin early clinical testing of a possible target for breast cancer stem cells. No standard treatments have yet been developed as a result of cancer stem cell research.

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Read about stem cell research at the University of Michigan:

Stem Cells - Explained and Explored

More stem cells resources:

National Institutes of Health Web site on stem cells

International Society for Stem Cell Research

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