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I am not a science major, but my understanding is that it takes at least 2 genetic mutations to cause cancer. A good example is that not everyone with the BCA-1 gene develops breast cancer. That gene has been identified as a contributing factor, but another genetic mutation must occur before cancer occurs. Another example is not everyone who smokes cigarettes develops lung cancer. Smoking does cause a genetic mutation, but another genetic mutation must happen before you get cancer.
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