Bacteria as anticancer agents. For many years, bacteria and their toxins have been investigated for their anticancer activities. In the 1970s, bacteria (such as non-pathogenic Clostridium) were used for the treatment of malignant brain tumors. While the therapy was successful in the short term, the tumors recurred in these brain tumor patients. Subsequent to this initial work, more than 100 microorganisms have been studied for their potential anticancer activities. Interestingly, many bacteria have a growth specificity for tumors that is 1000 times greater than for other tissue.