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 favour. Over the past 20 years, investigators have linked several types of cancer to viruses, bacteria or parasites. According to the Scientific American, about five per cent 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. Other CanWest Global Communications Corp. Sites Our privacy policy .