Medical Glossary O

Oat cell cancer: A type of lung cancer in which the cells look like oats. Also called small cell lung cancer.

Oligodendroglioma (OL-ih-go-den-dro-glee-O-ma): A rare, slow growing type of brain tumor that occurs in the cells that produce myelin, the fatty covering that protects nerves.

Ommaya reservoir (o-MYE-a REZ-er-vwahr): A device implanted under the scalp and used to deliver anticancer drugs to the fluid surrounding the brain and spinal cord.

Oncogene: The part of the cell that normally directs cell growth, but which can also promote or allow the uncontrolled growth of cancer if damaged (mutated) by an environmental exposure to carcinogens, or damaged or missing because of an inherited defect.

Oncology: The study of tumors encompassing the physical, chemical, and biologic properties.

Oophorectomy (oo-for-EK-to-mee): The removal of one or both ovaries.

Ophthalmoscope (off-THAL-mo-skope): A lighted instrument used to examine the inside of the eye, including the retina and the optic nerve.

Optic nerve: The nerve that carries messages from the retina to the brain.

Oral Cavity Cancer: Cancer of the lip and oral cavity is a disease in which cancer (malignant) cells are found in the tissues of the lip or mouth. The oral cavity includes the front two-thirds of the tongue, the upper and lower gums (the gingiva), the lining of the inside of the cheeks and lips (the buccal mucosa), the bottom (floor) of the mouth under the tongue, the bony top of the mouth (the hard palate), and the small area behind the wisdom teeth (the retromolar trigone).

Oral surgeon: A dentist with special training in surgery of the mouth and jaw.

Orchiectomy (or-kee-EK-to-mee): Surgery to remove the testicles.

Organisms: Plants, animals, and other forms of life that are made up of complex and interconnected systems of cells and tissue.

Oropharynx (or-o-FAIR-inks): The area of the throat at the back of the mouth.

Osteosarcoma (OSS-tee-o-sar-KO-ma): A cancer of the bone that is most common in children. Also called osteogenic sarcoma. It is the most common type of bone cancer.

Ostomy (AHS-toe-mee): An operation to create an opening from an area inside the body to the outside. See Colostomy.

Otolaryngologist (AH-toe-lar-in-GOL-o-jist): A doctor who specializes in treating diseases of the ear, nose, and throat.

Ovarian Cancer: Cancer of the ovary is a disease in which cancer (malignant) cells are found in the ovary. Approximately 25,000 women in the United States are diagnosed with this disease each year. The ovary is a small organ in the pelvis that makes female hormones and holds egg cells which, when fertilized, can develop into a baby.

Ovaries (O-var-eez): The pair of female reproductive glands in which the ova, or eggs, are formed. The ovaries are located in the lower abdomen, one on each side of the uterus.