Clostridium novyi is a genetically altered
bacteria. The bacteria is normally potentially fatal when introduced into a biological entity, but this version is altered to not reproduce in a way that allow the
neurotoxin to be produced. Otherwise, it would have induced
botulism. For more info on the original bacteria, see
Clostridium botulinum.
Now comes the interesting part. This spore-type bacteria thrives in enviroments with little oxygen, since it's an anaerobe. Cancer tissue is typically very dense and oxgygen-poor. Researchers at John Hopkins institute have carried out an experiment on mice with human cancer tumors, and discovered that the Cl. novyi bacteria is extremly efficient in treating cancer this way. Combined with chemotherapy, the tumors actually disappeared from 50% of the mice. The bacteria damaged none of the surrounding tissue. Researchers are optimistic about human experiments within a few years.