Tumor is an abnormal growth of tissues in the body. Tumors are also called neoplasms. Some tumors are benign. They limit themselves to a certain region and do not spread elsewhere in the body. Once benign tumors are removed, they usually do not grow again. Malignant tumors (cancers) that are not completely removed can spread throughout the body, often destroying other tissues in the body. See Cancer (How damaged genes cause cancer). When cancer arises from the skin, tissues that line the body cavities, or nonblood-forming organs, it is called carcinoma. Cancer that affects bones, cartilages, and soft tissues is called sarcoma. Leukemia is cancer of the bone marrow or other blood-forming organs. Only a doctor can determine whether a tumor is benign or malignant.
Tumors may grow from any kind of tissue in the body. They may develop in the skin, muscles, nerves, blood vessels, bones, or any organ. A well-known tumor is the mastoid tumor, which grows over the mastoid process just behind the ear.
Tumors are often named after the tissue from which they grow. For example, a lipoma is a benign tumor made up of lipid (fat) tissue. Gliomas (nerve-tissue tumors) are made up of glia, the branched cells that support the nerves. Lymphoma is a malignant tumor of lymphoid tissue. It is one of the best-studied tumors, and it is highly treatable by chemotherapy and radiation therapy.
