Bacterial infection and human cancer: association or causation?

Environmental factors such as diet, industrial pollution, smoking and viruses account for some 80% of cancers and more than one-quarter of all non-accidental deaths. Little attention has been paid to the relationship between bacterial infection and cancer but there is growing evidence to support this link. For some sites, such as stomach and colorectum, the evidence is relatively strong, whereas for others, such as biliary tract and bladder, it is more circumstantial.