hair follicles (FOL-i-kuls): Shafts or openings on the surface of the skin through which hair grows.

hairy cell leukemia: A type of chronic leukemia in which the abnormal white blood cells appear to be covered with tiny hairs when viewed under a microscope.

hawthorn fruit: The fruit of the hawthorn bush. It has been used in some cultures to treat certain medical problems, including heart problems and gastrointestinal problems.

Hedyotis diffusa: An herb used in traditional Chinese medicine to treat certain medical problems. It has been used to boost the immune system and may have anticancer effects.

Helicobacter pylori (HEEL-ih-ko-BAK-ter pye-LOR-ee): Bacteria that cause inflammation and ulcers in the stomach.

hemangiopericytoma: A type of cancer involving blood vessels and soft tissue.

hematogenous: Originating in the blood or spread through the bloodstream.

hematologic malignancies: Cancers of the blood or bone marrow, including leukemia and lymphoma. Also called hematologic cancers.

hematologist (hee-ma-TOL-o-jist): A doctor who specializes in treating diseases of the blood.

hematopoiesis: The forming of new blood cells.

hematopoietic growth factors: A group of proteins that cause blood cells to grow and mature.

hematopoietic tissue: Tissue in which new blood cells are formed.

hematoporphyrin derivative: A drug used in photodynamic therapy that is absorbed by tumor cells. When exposed to light, it becomes active and kills the cancer cells.

hemophilia: Refers to a group of hereditary disorders in which affected individuals fail to make enough of certain proteins needed to form blood clots.

hemorrhoid: An enlarged or swollen blood vessel, usually located near the anus or the rectum.

heparin: A drug that helps prevent blood clots from forming. It belongs to the family of drugs called anticoagulants (blood thinners).

hepatic: Refers to the liver.

hepatitis (hep-a-TYE-tis): Inflammation of the liver.

hepatitis B: A type of hepatitis that is carried and passed to others through the blood or sexual contact.

hepatoblastoma (HEP-a-toe-blas-TOE-ma): A type of liver tumor that occurs in infants and children.

hepatocellular carcinoma (HEP-a-toe-SEL-yoo-ler kar-sin-O-ma): A type of adenocarcinoma, the most common type of liver tumor.

hepatocyte (HEP-a-toe-site): A liver cell.

hepatoma (hep-a-TOE-ma): A liver tumor.

HER2/neu: Human epidermal growth factor receptor 2. The HER2-neu protein is involved in growth of some cancer cells. Also called c-erbB-2.

HER2/neu gene: The gene that makes the human epidermal growth factor receptor 2. The protein produced is HER2/neu antigen, which is involved in the growth of some cancer cells. Also called c-erbB-2.

herbicide: A chemical that kills plants.

hereditary mutation: A gene change in the body's reproductive cells (egg or sperm) that becomes incorporated into the DNA of every cell in the body of offspring; hereditary mutations are passed on from parents to offspring. Also called germline mutation.

hereditary nonpolyposis colon cancer: An inherited disorder in which affected individuals have a higher-than-normal chance of developing colon cancer and certain other types of cancer, usually before the age of 60. Also called Lynch syndrome.

herpes virus (HER-peez VYE-rus): A member of the herpes family of viruses.

heterogenic (het-er-o-JEN-ik): Derived from a different source or species. Also called heterogenous.

heterogenous: Derived from a different source or species. Also called heterogenic.

high-grade lymphomas: Includes large cell, immunoblastic, lymphoblastic, and small noncleaved cell lymphomas. These lymphomas grow quickly but have a better response to anticancer drugs than that seen with low-grade lymphomas.

histamine dihydrochloride: A drug being studied for its ability to enhance the effectiveness of IL-2 in treating acute myeloid leukemia.

histology: The study of tissues and cells under a microscope.

HIV: Human immunodeficiency virus, the cause of acquired immunodeficiency syndrome (AIDS).

HIV antibody: A substance produced by certain white blood cells in reaction to contact with HIV, the human immunodeficiency virus.

Hodgkin's disease: A malignant disease of the lymphatic system that is characterized by painless enlargement of lymph nodes, the spleen, or other lymphatic tissue. It is sometimes accompanied by symptoms such as fever, weight loss, fatigue, and night sweats.

holmium Ho 166 DOTMP: A drug containing a radioactive isotope that is used in the diagnosis and treatment of cancer.

homeopathic remedies: Small doses of medicines, herbs, or both that are believed to stimulate the immune system.

homoharringtonine: An anticancer drug that belongs to the plant alkaloid family of drugs.

hormonal therapy: Treatment of cancer by removing, blocking, or adding hormones. Also called hormone therapy or endocrine therapy.

hormone receptor test: A test to measure the amount of certain proteins, called hormone receptors, in cancer tissue. Hormones can attach to these proteins. A high level of hormone receptors may mean that hormones help the cancer grow.

hormone replacement therapy: HRT. Hormones (estrogen, progesterone, or both) given to postmenopausal women or women who have had their ovaries surgically removed, to replace the estrogen no longer produced by the ovaries.

hormone therapy: Treatment of cancer by removing, blocking, or adding hormones. Also called endocrine therapy.

hormones: Chemicals produced by glands in the body and circulated in the bloodstream. Hormones control the actions of certain cells or organs.

Horner's syndrome: A condition in which one side of the face is flushed, does not produce sweat, and has a constricted pupil and drooping eyelid. It can be caused by an injury to, or paralysis of, nerves in the neck, or by a tumor.

hu14.18-interleukin-2 fusion protein: An anticancer drug in which hu14.18, a monoclonal antibody, is combined with interleukin-2. The monoclonal antibody binds to the cancer cells and delivers IL-2, which stimulates the immune system to destroy the cancer cells.

Huang Lian: A Chinese herb that has been used as a treatment for a variety of medical problems. It is being studied as an anticancer drug.

human papillomavirus (pap-ih-LO-ma VYE-rus): HPV. A virus that causes abnormal tissue growth (warts) and is often associated with some types of cancer.

humidifier (hyoo-MID-ih-fye-er): A machine that puts moisture in the air.

Hürthle cell neoplasm (HER-tel cell): An uncommon type of thyroid tumor that can be benign or malignant.

hydration: Combining with water.

hydrazine sulfate: A substance that has been studied as a treatment for cancer and as a treatment for cachexia (body wasting) associated with advanced cancer.

hydrocephalus (hye-dro-SEF-uh-lus): The abnormal buildup of cerebrospinal fluid in the ventricles of the brain.

hydrocortisone: A drug used to relieve the symptoms of certain hormone shortages and to suppress an immune response.

hydrogen peroxide: A chemical used in bleaches, dyes, cleansers, antiseptics, and disinfectants. In a concentrated form, it is toxic and irritating to tissues.

hydrolysis: A chemical reaction that uses water to break down a compound.

hydromorphone: A drug used to relieve pain.

hydronephrosis: Abnormal enlargement of a kidney, which may be caused by blockage of the ureter (such as by a kidney stone) or chronic kidney disease that prevents urine from draining into the bladder.

hydroureter: Abnormal enlargement of the ureter caused by any blockage that prevents urine from draining into the bladder.

hydroxyurea: An anticancer drug that belongs to the family of drugs called antimetabolites.

hyperbaric oxygen: Oxygen that is at an atmospheric pressure higher than the pressure at sea level. Breathing hyperbaric oxygen to enhance the effectiveness of radiation therapy is being studied.

hypercalcemia (hye-per-kal-SEE-mee-a): Abnormally high blood calcium.

hyperfractionation: A way of giving radiation therapy in smaller-than-usual doses two or three times a day instead of once a day.

hyperglycemia: Abnormally high blood sugar.

hyperplasia (hye-per-PLAY-zha): An abnormal increase in the number of cells in an organ or tissue.

hypersensitivity: An exaggerated response by the immune system to a drug or other substance.

hypertension: Abnormally high blood pressure.

hyperthermia (hye-per-THER-mee-a): A type of treatment in which body tissue is exposed to high temperatures to damage and kill cancer cells or to make cancer cells more sensitive to the effects of radiation and certain anticancer drugs.

hyperthermic perfusion: A procedure in which a warmed solution containing anticancer drugs is used to bathe, or is passed through the blood vessels of, the tissue or organ containing the tumor.

hyperthyroidism: A condition in which the thyroid gland produces too much thyroid hormone.

hyperuricemia: A buildup of uric acid (a byproduct of metabolism) in the blood; a side effect of some anticancer drugs.

hypervascular: Having a large number of blood vessels.

hypoglycemia: Abnormally low blood sugar

hypopharynx: The bottom part of the throat. Cancer of the hypopharynx is also called hypopharyngeal cancer.

hypotension: Abnormally low blood pressure.

hypothalamus (hye-po-THAL-uh-mus): The area of the brain that controls body temperature, hunger, and thirst.

hypothesis: A tentative proposal made to explain certain observations or facts that requires further investigation to be verified.

hypoxic: Having too little oxygen.

hysterectomy (hiss-ter-EK-toe-mee): An operation in which the uterus is removed.