A vital protein, perhaps, is being altered or destroyed as one cell divides to create another. The mutated cell, an incorrect version of its former self, will continue to multiply, compounding and extending its grotesque influence as an intruder and usurper, bent on its own self- preservation at your expense. It has become cancer.

 

Such malignant transformation is one of the biggest threats to multicellular organisms, and evolution has favored a wide range of genetic defenses against it. Your cells are equipped with regulatory mechanisms that keep routine division and differentiation on a tight leash, with tumor-suppressor proteins and DNA-repair genes that can correct damage,