For more than 60 years, robert Martensen's lung cells replicated without a hitch, regulated by specialized enzymes called kinases. Much like thermostats that adjust the temperature in a room to make sure it's not too hot or too cold, kinases make sure that the right number of new cells are created as old ones die. But sometime in his early sixties, something changed inside Martensen. One or more of the genes coding for his kinases mutated, causing his lung cells to begin replicating out of control. At first the clusters of rogue cells were so small that Martensen had no idea they existed. Nor was anyone looking for them inside the lean, ruddy-faced physician, who exercised most days and was an energetic presence as the chief historian at the National Institutes of Health.
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