Researchers estimate that viruses and bacteria play a role in the development of about 20 % of all new cancer cases. So, e.g. unambiguous connections between Humanen Papilloma viruses (HPV) and cervical cancer have been determined. In the development of cancer, viruses often appear co-factors of further causes. Environmental influences and errors in the genetic programme and cell division bear essential responsibility. Also smoking, excessive consume of alcohol, and overweight are known risk factors.
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