Effective
cancer treatment is an urgent need due to the rising incidence of
cancer. One of the most promising future strategies in
cancer treatment is using microorganisms as
cancer indicators, prophylactic agents, immune activators,
vaccines or vectors in antitumor
therapy. The success of bacteria-mediated
chemotherapy will be dependent on the balance of therapeutic benefit and the control of
bacterial infection in the body. Additionally, protozoans and viruses have the potential to be used in
cancer therapy. This review summarizes how these microorganisms interact with tumor microenvironments and the challenges of a 'bugs as drugs' approach in
cancer therapy. Several standpoints are discussed, such as bacteria as vectors for gene therapy that shuttle therapeutic compounds into
tumor tissues, their intrinsic antitumor activities and their combination with
chemotherapy or
radiotherapy. Bug-based
cancer therapy is a two-edged sword and we need to find the opportunities by overcoming the challenges.