National Cancer Institute
In the mid-1990s, Canadian researchers discovered the first cancer-initiating cells in patients with acute myeloid leukemia. These so-called cancer stem cells, which make up less than five percent of a tumor, may, in fact, be the cells that are the earliest precursors of cancer’s spread and the cells most resistant to conventional treatments.
In the years since that initial discovery, cancer stem cells have been identified in other blood-borne cancers, along with brain, breast, ovarian, and, most recently, colon cancers. By any measure, the science of cancer stem cells is both a young avenue of investigation and an extremely promising one. Scientists believe that some tumors contain small populations of these self-renewing cells. They also note that the tumor microenvironment is crucial to a complete understanding of stem cells, as the microenvironment’s noncancerous host tissue plays a major role in cancer progression, in the nourishment of the tumor, and in its ability to communicate.
NCI supports research to isolate cancer stem cells, based on markers that are shared by normal tissue stem cells of the same type — and occasionally by other cells, as well. The hope is that scientists can develop therapies that target and control cancer stem cells before they lead to metastasis — or, via some fascinating new insights, engineer certain other tissue stem cells to create healthy organs.
Among the many investigators NCI supports across the United States is Anthony Atala, M.D., from Wake Forest University, a leader in the emerging field of tissue engineering using stem cells. Recently, Dr. Atala isolated stem cells through a procedure familiar to millions of expectant mothers: amniocentesis. This common technique, normally performed about 16 weeks into pregnancy, tests the fluid that surrounds a growing fetus for signs of genetic disorders. As Dr. Atala has noted, amniotic fluid cells are also proving useful for other areas of scientific study and may, in time, be therapeutically valuable, since they will not form tumor cells, as embryo-derived cells can. Furthermore, because they grow slowly, amniotic fluid cells can also be more readily controlled.
It is important to remember that cancer stem cells have only recently been discovered. As a cautionary example, a recent scientific publication suggests that many more tumor cells have tumor initiating potential than previously thought. To answer fundamental questions about cancer stem cells, scientists will need to develop more efficient techniques for isolating the cells and maintaining them in culture, as Dr. Atala has done. Single-cell analyses will also likely be needed to distinguish events present in cancer stem cells from the more differentiated cells that make up the majority of the tumor.
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