Sarcomas are cancers of the supporting tissues of the body, such as bone, muscle and blood vessels. Cancers of the blood and the lymph glands are called leukemias and lymphomas, respectively. Gliomas are cancers of the nerve tissue.
Melanomas arise from darkly pigmented cells, usually in the skin.
Cancer occurs when the DNA present in a gene is altered in such a way that the gene can no longer instruct the cell in which it resides to produce a certain protein in the normal manner. Such an alteration can take place when a gene is exposed to radiation or particular drugs or chemicals, or when some as yet unexplained internal signal occurs. These factors can cause the DNA within a gene to break and recombine incorrectly or to mutate. If a gene has become an oncogene, the cell in which it is located may begin to produce unusually large amounts of one of its normal proteins or to manufacture an altered form of that protein. If an anti-oncogene has been rendered inactive, the cell containing it can no longer produce a normal protein whose function is to suppress cancer.