Tumor: An abnormal mass of tissue. Tumors are a classic sign of inflammation, and can be benign or malignant (cancerous). There are dozens of different types of tumors. Their names usually reflect the kind of tissue they arise in, and may also tell you something about their shape or how they grow. For example, a medulloblastoma is a tumor that arises from embryonic cells (a blastoma) in the inner part of the brain (the medulla). Diagnosis depends on the type and location of the tumor. Tumor marker tests and imaging may be used; some tumors can be seen (for example, tumors on the exterior of the skin) or felt (palpated with the hands).

Treatment is also specific to the location and type of the tumor. Benign tumors can sometimes simply be ignored, or they may be reduced in size (debulked) or removed entirely via surgery. For cancerous tumors, options include chemotherapy, radiation, and surgery. See also blastoma, carcinoembryonic antigen test, desmoid tumor, ear tumor, epidermoid carcinoma, epithelial carcinoma, esophageal cancer, syringoma, fibroid, tumor marker.

Radiation: 1. Rays of energy. Gamma rays and X-rays are two of the types of energy waves often used in medicine. 2. The use of energy waves to diagnose or treat disease. See also: Irradiation.

Tissue: A tissue in medicine is not like a piece of tissue paper. It is a broad term that is applied to any group of cells that perform specific functions. A tissue in medicine need not form a layer. Thus,

• The bone marrow is a tissue;
• Connective tissue consists of cells that make up fibers in the framework supporting other body tissues; and
• Lymphoid tissue is the part of the body's immune system that helps protect it from bacteria and other foreign entities.

Radiation therapy: The use of high-energy rays to damage cancer cells, stopping them from growing and dividing. Like surgery, radiation therapy is a local treatment that affects cancer cells only in the treated area.

Radiation can come from a machine (external radiation or from an a small container of radioactive material implanted directly into or near the tumor (internal radiation). Some patients receive both kinds of radiation therapy. External radiation therapy is usually given on an outpatient basis in a hospital or clinic, five days a week for several weeks. Patients are not radioactive during or after the treatment. For internal radiation therapy, the patient stays in the hospital for a few days. The implant may be temporary or permanent. Because the level of radiation is highest during the hospital stay, patients may not be able to have visitors, or may have visitors only for a short time. Once an implant is removed, there is no radioactivity in the body. The amount of radiation in a permanent implant goes down to a safe level before the patient leaves the hospital.

Side effects of radiation therapy depend on the treatment dose and the part of the body that is treated. The most common side effects are tiredness, skin reactions (such as a rash or redness) in the treated area, and loss of appetite. Radiation therapy can cause inflammation of tissues and organs in and around the body site radiated. Radiation therapy can also cause a decrease in the number of white blood cells. Although the side effects of radiation therapy can be unpleasant, they can usually be treated or controlled. It also helps to know that, in most cases, they are not permanent.

Prostate cancer: An uncontrolled (malignant) growth of cells in the prostate gland which is located at the base of the urinary bladder and is responsible for helping control urination as well as forming part of the semen. Prostate cancer is the second leading cause of death of males in the U.S.