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More evidence that tumours, like healthy organs, grow from stem cells

THE notion that tumours are chaotic masses of anarchic cells has been falling by the wayside recently. Many researchers now think, by contrast, that cancers actually resemble normal, well-regulated organs in several important ways. One of these is that they are believed to have a small population of stem cells which keep them going when other cells die or are killed off. The existence of such cancer stem cells is still a matter of debate. But this week the discussion may have taken an important turn. Brid Ryan, Sharon Pine and Curtis Harris, of America’s National Cancer Institute, reported that some lung-cancer cells do, indeed, seem to behave like stem cells during the process of cell division.

Unlike normal cells, stem cells can divide in two different ways. They may do so symmetrically, thereby producing identical daughter cells, each of which resembles the mother cell. Or they may do so asymmetrically, and give rise to two very different daughters. In such cases, one of the daughters is identical to the original stem cell, while the other takes on new characteristics and can then differentiate into whatever cell type the tissue it inhabits requires. …

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