For example, if lung cancer spreads to the liver, the cancer cells in the liver are lung cancer cells. Our current understanding of what causes cancer is incomplete, but it is clear that cancer is not caused by an injury, such as a bump or bruise. Being infected with certain viruses may increase the risk of some types of cancer, but cancer is not contagious. Cancer develops gradually as a result of a complex mix of factors related to environment, life style, and heredity. Scientists have identified many risk factors that increase the chance of getting cancer.
Some people are more sensitive than others to factors that can cause cancer.
Many risk factors can be avoided. Others, such as inherited risk factors, are unavoidable. How cancer is diagnosed After a physical exam, the doctor will order various tests and exams. In most cases, the doctor may order a biopsy, a procedure in which a sample of tissue is removed. A pathologist examines the tissue under a microscope to check for cancer cells.