Researchers noticed early on that rapamycin slowed the growth of cancer cells in the test tube.

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Dr Reynolds, and others, have shown that under the influence of suitable growth factors, stem cells can lead full lives in a test tube.

ECONOMIST: Something new in mind

Sure enough, he found that the only cells that could produce new tumors in the test tube were the ones with CD133--strong circumstantial evidence that defective stem cells were the growth factor in brain cancer.

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