• Stem cells: A primer

    A stem cell is a biological blank slate that can spawn many types of cells in the body. The most generic and powerful stem cells are embryonic stem cells, found in the embryo soon after conception. They can create all 200 cell types, including blood, bone, skin, muscle, and nerve.

    Stem cells not only generate specific kinds of cells, they also have the power of "self-renewal." Unlike regular cells, which divide a certain number of times and then die, stem cells can turn out identical copies of themselves virtually forever.

    Embryonic stem cells disappear when their work is done, but even after the body is fully formed, adult stem cells remain to replenish specific cell types that are lost or damaged. Adult stem cells are more limited in the types of cells they can generate, but they can be used in research without the ethical controversy involved in obtaining stem cells from human embryos, which are destroyed in the process. Because stem cells are so versatile, scientists are working to harness them for replacement tissues in patients with neurodegenerative diseases like Parkinson's and Alzheimer's.

    The hypothesized "cancer stem cell" is a mutated, corrupted adult stem cell that has cancer-causing properties and is self-renewing, making it a dangerous renegade that some scientists blame for causing treated cancers to recur. According to the hypothesis, solid tumors contain a small cadre of cancer stem cells that often survive therapy, lurking silently to regrow months or years after treatment to form another tumor.

    Scientists continue to debate whether these cancer stem cells are truly the root of all evil in tumors. Nevertheless, the National Cancer Institute and other funding sources continue to support research that, in time, should answer such questions.

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