How cancer starts: how a normal cell turns into cancer
Moles: most carry a cancer mutation, so why do they stop growing?
Four out of five ordinary moles carry the same broken gene as many melanomas, a dangerous skin cancer. Most people have many moles, and almost none of them ever become cancer. What holds them back?
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Here is a surprise. In 2003, researchers read the DNA of 77 ordinary moles. In 63 of them, about four in five, BRAF was jammed, the same mistake as in Rono's mole. It is also the mistake found in many melanomas, a skin cancer.
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And yet a mole almost never turns into melanoma. Most adults have between 10 and 40 moles. They stop growing, and almost all of them never become cancer. So something holds them back.
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To see what, go back fifty years, into Rono's skin. With BRAF jammed, his pigment cell copied with no message, again and again, much faster than normal.
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But copying that fast, with no message, is a danger sign. It woke up the brakes inside the cells: the tumour suppressor genes. They pressed down hard.
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The brakes did more than slow the cells down. They stopped them, usually for life. The cells stay alive and keep making pigment, but they almost never copy again. Scientists call this kind of stop senescence.
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That is why Rono's mole stayed the same size for fifty years: a family of cells with a jammed accelerator, held still by its brakes. One mutation, even a cancer mutation, was not enough.
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Now Rono's mole is growing again. Cells that had stopped for fifty years are copying. For fifty years the brakes held. What finally broke them, and what can the cells do now?
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Quick check
Cells in a dish.
Show the answer
No. After a while, their brakes stop them, and the stop lasts: senescence. Scientists think something like this holds the cells of a mole.
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Go further
Two names, and one surprise.