Approximately 70-80 percent of cancers in the aging population are the result of

Cigarette smoking and environmental chemicals

Tobacco smoke and certain environmental chemicals are known carcinogens (substances that can cause cancer in living tissue). The tobacco smoke from cigarette smoking contains harmful chemicals such as hydrogen cyanide, arsenic, ammonia, benzene, and many more. In fact, from 2009 to 2013, three out of 10 cancer deaths in the U.S have been attributed to cigarette smoking or exposure to tobacco smoke. 

The gens present in the dna in the nucleus of the cell in the body