We have been long conceived that cancer cells are formed from developing oncogenic mutations during proliferation. On the other hand, it is very natural to think that normal tissue cells should have no or maybe very few (just to make it not too absolute) mutations. However, the latest Science paper by Martincorena et al . suggests that normal skin tissues do carry oncogenic mutations, in an amount that may be higher than you thought. The group of scientists collected 234 biopsies of normal eyelid skin tissues from 4 individuals and sequenced 74 known cancer genes in them. What they've found is that the mutation rate of these genes in the sequenced skin tissues is actually as high as in many type of cancer tissues! It is comparable to the mutation rates of breast cancer and is only a factor of 10 less than that in a type of skin carcinoma! How do healthy people, including us, have so many mutations in normal skin tissues? The answer is: sunlight. The study looked into specific ...