In the decades that followed, their attempts to verify this theory failed. Introduction of various infections into animals usually did not yield cancer, according to the Scientific American. Gradually, the theory fell out of favor. Over the past 20 years, investigators have linked several types of cancer to viruses, bacteria or parasites. According to the Scientific American , about five percent of cancer fatalities in the U.S. result from diseases brought on by infections.
Researchers have yet to crack the code on the reasons cell growth spins out of control.
But chemicals, radiation, viruses, hormones and inherited mutations can act together to start or further cancer. See our privacy policy , terms of use , ad rates and legal notices . Voted best news site in California and Nevada by the Associated Press Television and Radio Association.