Carcinogenic bacteria

Cancer bacteria are bacteria infectious organisms that are known or suspected to cause cancer. While cancer-associated bacteria have long been considered to be opportunistic (i.e., infecting healthy tissues after cancer has already established itself), there is some evidence that bacteria may be directly carcinogenic. The strongest evidence to date involves the bacterium H. pylori and its role in gastric cancer.

Oncoviruses are viral agents that are similarly suspected of causing cancer.