We constantly live in a soup of bacteria and viruses.
Only a big nuke will get rid if these, temporarly.
Cancer is a genetic mutation which produces blood-greedy over-growth of normal cells in the wrong places at the wrong times.
Fight cancer with viruses:
http://www.nytimes.com/2012/03/20/health/research/viruses-are-recruited-and-flipped-as-cancer-killers.html
"Unlike chemotherapy, which can diminish in effectiveness over time, oncolytic viruses multiply in the body and gain strength as the infection becomes established. In addition to attacking cancer cells directly, some also produce an immune response that targets tumors."