Cancer arises in cells when the DNA becomes mutated in a way that the cells can’t repair itself. DNA mutations do occur at a low rate normally but cells can usually fix these without a problem. Cancer can either be caused genetically or environmentally. Some cancers happen because of an inherited mutation that increases the chance of getting cancer. Other cancers occur an environmental factor significantly increases the rate of DNA mutation. These factors include things like UV light (from excessive sunbathing/tanning beds) that can cause skin cancer, and smoking, which can cause lung cancer.