cancer

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WASHINGTON, Nov 20 (Reuters) Stem cells -- the master cells that give rise to all the blood and tissue in the body -- may also be responsible for tumors, according to two separate studies.

Canadian and Italian researchers both found that specialized colon cancer stem cells appeared to be the sources of colon cancer tumors in mice.

Their findings, published yesterday in the journal Nature, support the idea that future cancer treatments will have to home in on cancer stem cells.

Similar findings have been seen for leukemia, breast and brain cancers, but the two studies are the first to show cancer stem cells are also responsible for colon tumors.

''Colon cancer is one of the best-understood neoplasms (tumors) from a genetic perspective, yet it remains the second most common cause of cancer-related death (in Canada), indicating that some of its cancer cells are not eradicated by current therapies,'' John Dick of University Health Network in Toronto and colleagues wrote in their report.

They implanted human colon cancer cells into mice with a deficient immune system -- a standard way of studying cancer.

Only certain cells, those with a protein on the surface called CD133, were able to initiate a new tumor.

CD133 had previously been implicated in brain and prostate cancers. In a second study, Ruggero De Maria of the Istituto Superiore di Sanita in Rome and colleagues got the same CD133 cells to start tumors when injected under the skin of immune-deficient mice.

''These studies demonstrate that a small population of colon cancer cells, distinct from those that make up the bulk of a tumor, initiate tumor growth,'' Nature said in a statement.

It may be possible to design drugs that attack only those cells, and thus treat colon cancer in a way that better affects the tumors without hurting healthy cells, the researchers said.

Colon cancer is the fourth most deadly cancer globally, killing 655,000 people a year, according to the World Health Organization.