Etiology is the study of causation, or origination. Cancer is neither contagious nor hereditary disease. It is suggested that every living organism has some inactive cancer-causing genes called proto-oncogenes. A number of physical, chemical or biological agents are known to mutate and activate these proto-oncogenes into active and cancer causing oncogenes. Due to altered gene activity, normal control mechanism is lost and the abnormal cell growth and cell division take place. Cancer can be caused by radiations, physical irritants and chemical or biological agents.