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 lympkemia 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.

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

Hematopoietic tissue: Blood-forming tissue, consisting of reticular fibers and cells.

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): HCC, also called malignant hepatoma, is a primary malignancy (cancer) of the liver. Most cases of HCC are secondary to either a viral hepatitide infection (hepatitis B or C) or cirrhosis (alcoholism being the most common cause of hepatic cirrhosis).

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

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

HER2/n: 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 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.