Carcinogenesis and Leukemogenesis of Microorganisms: A Review

Several studies have shown that microorganisms can affect tumor initiation and progression, directly through their effects on the cells and indirectly by their effects on the immune system. The carcinogenesis of certain viral, bacterial, fungal, and parasitic organisms has been long suspected. Additionally, the direct association of some viral agents and cancer such as Epstein-Barr virus and Burkitt’s lymphoma, in certain geographical areas, have been reported. Likewise, the development of non-cardia gastric cancer by Helicobacter pylori and the relation of infection with Schistosoma haematobium and the development of bladder cancer is well recognized. Studies regarding the carcinogenetic effects of fungal infections have been mostly attributed to their mycotoxin production. Recent recognition that some filamentous fungi and yeasts potentially play a role in the development of certain cancers has expanded understanding of the scope of their involvement in carcinogenesis. Most recently, it has been shown that plasma of patients with B-cell acute lymphoblastic leukemia in full remission, and long-term survivors, immunologically react to the products of a mycovirus containing Aspergillus flavus. Unlike controls, in vitro exposure of mononuclear leukocytes from these patients to the products of this organism was shown to reproduce genetic and cell surface phenotypes characteristic of B-cell acute lymphoblastic leukemia. The potential carcinogenic and leukemogenic role of fungi, with and without mycoviruses, needs further investigation.