Cancer Glossary - O

O(6)-benzylguanine   A drug that may improve the response of cancer cells to chemotherapy.

oat cell cancer   A type of lung cancer in which the cells look like oats when viewed under a microscope. Also called small cell lung cancer.

oblimersen   A drug that may kill cancer cells by blocking the production of a protein that makes cancer cells live longer. Also called bcl-2 antisense oligodeoxynucleotide G3139 and augmerosen.

observation   Closely monitoring a patient's condition but withholding treatment until symptoms appear or change. Also called watchful waiting.

obstruction   Blockage of a passageway.

obtundation  (ob-tun-DAY-shun) A dulled or reduced level of alertness or consciousness.

octreotide   A drug similar to the naturally occurring growth hormone inhibitor somatostatin. Octreotide is used to treat diarrhea and flushing associated with certain types of tumors.

ofloxacin   An antibiotic drug used to treat infection. It belongs to the family of drugs called quinolone antibiotics.

olbimersen   A drug that may kill cancer cells by blocking the production of a protein that makes cancer cells live longer. Also called bcl-2 antisense oligodeoxynucleotide G3139.

oligodendroglial tumors   Rare, slow-growing tumors that begin in brain cells called oligodendrocytes, which provide support and nourishment for cells that transmit nerve impulses. Also called oligodendroglioma.

oligodendroglioma  (OL-ih-go-den-dro-glee-O-ma) A rare, slow-growing tumor that begins in brain cells called oligodendrocytes, which provide support and nourishment for cells that transmit nerve impulses. Also called oligodendroglial tumor.

oltipraz   A drug used in cancer prevention.

omega-3 fatty acid   A type of fat obtained in the diet and involved in immunity.

omentectomy   Surgery to remove part or all of the omentum.

omentum  (oh-MEN-tum) A fold of the peritoneum (the thin tissue that lines the abdomen) that surrounds the stomach and other organs in the abdomen.

omeprazole   A drug that inhibits gastric acid secretion.

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

oncogene   A gene that normally directs cell growth. If altered, an oncogene can promote or allow the uncontrolled growth of cancer. Alterations can be inherited or caused by an environmental exposure to carcinogens.

oncologist  (on-KOL-o-jist) A doctor who specializes in treating cancer. Some oncologists specialize in a particular type of cancer treatment. For example, a radiation oncologist specializes in treating cancer with radiation.

oncology   The study of cancer.

oncology nurse   A nurse who specializes in treating and caring for people who have cancer.

oncology pharmacy specialist   A person who works with an oncologist to prepare anticancer drugs.

oncolysate   An extract made from cancer cells that are infected with a lytic strain of virus. The extract contains both cancer cell proteins and virus proteins. Oncolysates are being studied as cancer vaccines.

oncolysis   The breakdown, or lysis, of a tumor. This can occur by mechanical means, chemicals, or infectious agents such as viruses. Oncolytic viruses do not lyse most normal cells.

ondansetron   A drug that prevents or reduces nausea and vomiting. It belongs to the family of drugs called antiemetics.

onset of action   The length of time it takes for a medicine to start to work.

ONYX-015   A modified cold virus that selectively grows in and destroys certain types of cancer cells and leaves normal cells undamaged.

oophorectomy  (o-o-for-EK-toe-mee) Surgery to remove one or both ovaries.

open colectomy   An operation to remove the colon through a surgical incision made in the wall of the abdomen.

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

opioids   A family of synthetic drugs used to treat moderate to severe pain. They are similar to opiates such as morphine and codeine.

optic nerve   The nerve that carries messages from the retina to the brain.

oral   By or having to do with the mouth.

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

orchiectomy  (or-kee-EK-toe-mee) Surgery to remove one or both testicles.

organism   A living thing, such as an animal, a plant, a bacterium, or a fungus.

oropharynx  (or-o-FAIR-inks) The middle part of the throat that includes the soft palate, the base of the tongue, and the tonsils.

osteogenic sarcoma   A cancer of the bone that affects primarily children and adolescents. Also called osteosarcoma.

osteolytic   Causing the breakdown of bone.

osteoporosis  (OSS-tee-oh-pa-ROW-sis) A condition that is characterized by a decrease in bone mass and density, causing bones to become fragile.

osteosarcoma  (AHS-tee-o-sar-KO-ma) A cancer of the bone that affects primarily children and adolescents. Also called osteogenic sarcoma.

ostomy  (AHS-toe-mee) An operation to create an opening (a stoma) from an area inside the body to the outside. Colostomy and urostomy are types of ostomies.

otolaryngologist  (AH-toe-lar-in-GOL-o-jist) A doctor who specializes in treating diseases of the ear, nose, and throat. Also called an ENT doctor.

outpatient   A patient who visits a health care facility for diagnosis or treatment without spending the night. Sometimes called a day patient.

ovarian   Having to do with the ovaries, the female reproductive glands in which the ova (eggs) are formed. The ovaries are located in the pelvis, one on each side of the uterus.

ovarian ablation   Surgery, radiation therapy, or a drug treatment to stop the functioning of the ovaries. Also called ovarian suppression.

ovarian epithelial cancer   Cancer that occurs in the cells lining the ovaries.

ovarian suppression   Surgery, radiation therapy, or a drug treatment to stop the functioning of the ovaries. Also called ovarian ablation.

ovaries  (O-va-reez) The pair of female reproductive glands in which the ova, or eggs, are formed. The ovaries are located in the pelvis, one on each side of the uterus.

over-the-counter   OTC. A medicine that can be bought without a doctor's order. Examples include some analgesics (pain relievers). Also called nonprescription.

overactive thyroid   Too much thyroid hormone. Symptoms include weight loss, chest pain, cramps, diarrhea, and nervousness. Also called hyperthyroidsm.

overall survival   The percentage of subjects in a study who have survived for a defined period of time. Usually reported as time since diagnosis or treatment. Also called the survival rate.

overexpress   An excess of a particular protein on the surface of a cell.

ovulation  (ov-yoo-LA-shun) The release of an egg from an ovary during the menstrual cycle.

oxaliplatin   An anticancer drug that belongs to the family of drugs called platinum compounds.

OXi-104   An anticancer drug being evaluated in combination with cisplatin.

oxidation   Process in which molecules are split to give products that have unpaired electrons.

oxidative metabolism   A chemical process in which oxygen is used to make energy from carbohydrates (sugars). Also known as aerobic respiration, cell respiration, or aerobic metabolism.

oxidative stress   A condition in which antioxidant levels are lower than normal. Antioxidant levels are usually measured in blood plasma.