ABSTRACT
The origin and host response to tumors is currently the focus of extensive basic and clinical research. With regard to origin, a large number of environmental factors have been shown to be carcinogenic and/or mutagenic in animals. Several tumors in humans have, in fact, been associated with exposure to certain substances (asbestos with mesotheliomas in shipyard workers, hydrocarbons with scrotal cancer in chimney sweeps, and smoking in lung cancer). Viruses are also known to induce tumors in animals and humans. In humans, the Epstein-Barr DNA virus is involved in Burkitt’s lymphoma and nasopharyngeal carcinoma, the hepatitis B virus in liver cancer, and the papillomavirus (HPV) in cervical carcinomas. The human T-lymphotropic virus 1 (HTLV-1, also known as human T-cell leukemia virus 1) is involved in certain forms of lymphocytic leukemia and human herpesvirus-8 (HHV-8) is associated with Kaposi’s sarcoma.
