Professor Robert Weinberg explains that cancer cells have to learn how to grow in the absence of growth stimulatory signals that normal cells require from their environment.

Cancer cells do not respond to signals that usually regulate cell growth and division. These cells grow unchecked, producing more and more cancer cells. Robert Weinberg, Ph.D., Whitehead Institute for Biomedical Research: “Cancer cells have to learn how to grow in the absence of growth stimulatory signals that normal cells require from their environment.” “Cancer cells have to learn how to grow in the presence of growth inhibitory signals that normally succeed in stopping the proliferation of normal cells.” In 2000, Douglas Hanahan (shown below) and Robert Weinberg published a paper in Cell, "The Hallmarks of Cancer," which identified some organizing principles of cancer cell development. “Not only are there positive signals that say grow but there are brakes which serve normally to stop such proliferation. And the loss of these growth control signals, these negative growth controls is again a common denominator for many cancers and this is separable in some sense from the growth stimulation, it's very much like putting your foot on the gas pedal, you put your foot on the gas pedal, the engine revs up, but if you've got your foot on the brake you still may not go anywhere. So these again are conceptually although they both relate to the ability of the cell to divide continuously they each have separable capabilities.”

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