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. 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.