# A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

O(6)-benzylguanine

A drug that may improve the response of cancer cells to chemotherapy.

oat cell cancer

An aggressive (fast-growing) cancer that usually forms in tissues of the lung and spreads to other parts of the body. The cancer cells look small and oval-shaped when looked at under a microscope. Also called small cell lung cancer.

obese

Having an abnormally high, unhealthy amount of body fat.

objective improvement

An improvement that can be measured by the health care provider (for example, when a tumor shrinks or there are fewer cancer cells in the blood).

objective response

A measurable response.

oblimersen

A substance that is being studied in the treatment of cancer. It may kill cancer cells by blocking the production of a protein that makes cancer cells live longer and by making them more sensitive to anticancer drugs. It belongs to the family of drugs called antisense oligodeoxyribonucleotides. Also called Genasense, augmerosen, and bcl-2 antisense oligodeoxynucleotide G3139.

observation

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

observational study

A type of study in which individuals are observed or certain outcomes are measured. No attempt is made to affect the outcome (for example, no treatment is given).

obstruction

Blockage of a passageway.

obtundation (ob-tun-DAY-shun)

A dulled or reduced level of alertness or consciousness.

occult stage non-small cell lung cancer

Cancer cells are found in sputum (mucus coughed up from the lungs), but no tumor can be found in the lung by imaging or bronchoscopy, or the primary tumor is too small to be assessed.

occupational therapist

A health professional trained to help people who are ill or disabled learn to manage their daily activities.

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.

octreotide scan

A type of radionuclide scan used to find carcinoid and other types of tumors. Radioactive octreotide, a drug similar to somatostatin, is injected into a vein and travels through the bloodstream. The radioactive octreotide attaches to tumor cells that have receptors for somatostatin. A radiation-measuring device detects the radioactive octreotide, and makes pictures showing where the tumor cells are in the body. This procedure is also called somatostatin receptor scintigraphy (SRS).

ocular melanoma

A rare cancer of melanocytes (cells that produce the pigment melanin) found in the eye. Also called intraocular melanoma.

off-label

Describes the legal use of a prescription drug to treat a disease or condition for which the drug has not been approved by the US Food and Drug Administration.

ofloxacin

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

OGF

Opioid growth factor. A substance made by the body and in the laboratory. It is being studied in the treatment of cancer. It belongs to the families of drugs called angiogenesis inhibitors and biological response modifiers.

OGX-011

A substance that is being studied as a treatment for cancer. It belongs to the family of drugs called antisense oligonucleotides.

oligoastrocytoma

A rare type of brain tumor made up of two kinds of cells, oligodendrocytes and astrocytes, which are brain cells that nourish and support nerve cells. Also called mixed glioma.

oligodendroglial tumor

A rare, slow-growing tumor that begins in the oligodendrocytes (brain cells that nourish and support nerve cells). Also called an oligodendroglioma.

oligodendroglioma (OL-ih-go-den-dro-glee-O-ma)

A rare, slow-growing tumor that begins in the oligodendrocytes (brain cells that nourish and support nerve cells). Also called an 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-MY-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.

oncolytic

Refers to viruses that kill cancer cells more often than they kill normal cells.

Onconase®

A substance that is being studied in the treatment of cancer. It belongs to the family of drugs called ribonuclease enzymes. Also called ranpirnase.

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 biopsy

A procedure in which a surgical incision (cut) is made through the skin to expose and remove tissues. The biopsy tissue is examined under a microscope by a pathologist. An open biopsy may be done in the doctor's office or in the hospital, and may use local anesthesia or general anesthesia. A lumpectomy to remove a breast tumor is a type of open biopsy.

open colectomy (ko-LEK-toe-mee)

An operation to remove all or part of the colon through a long incision made in the wall of the abdomen. When only part of the colon is removed, it is called a partial colectomy.

open label study

A type of study in which both the health providers and the patients are aware of the drug or treatment being given.

operable

Describes a condition that can be treated by surgery.

ophthalmic

Having to do with the eye.

ophthalmoscope (off-THAL-mo-skope)

A lighted instrument used to examine the inside of the eye, including the retina and the optic nerve.

opiate

A drug used to treat pain. It contains opium or a substance made from opium (such as morphine).

opioid

A drug used to treat moderate to severe pain. Opioids are similar to opiates such as morphine and codeine, but they do not contain and are not made from opium.

opioid growth factor (OH-pee-OYD grohth FAK-ter)

OGF. A substance made by the body and in the laboratory. It is being studied in the treatment of cancer. It belongs to the families of drugs called angiogenesis inhibitors and biological response modifiers.

opportunistic infection

An infection caused by an organism that does not normally cause disease. Opportunistic infections occur in people with weakened immune systems.

optic nerve

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

oral

By or having to do with the mouth.

oral and maxillofacial surgeon

A dentist who specializes in surgery of the mouth, face, and jaw.

oral cancer (OR-ul KAN-ser)

Cancer that forms in tissues of the lip or mouth. This includes the front two thirds of the tongue, the upper and lower gums, the lining inside the cheeks and lips, the bottom of the mouth under the tongue, the bony top of the mouth, and the small area behind the wisdom teeth.

oral cavity

The mouth.

oral surgeon

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

orchidectomy

Surgery to remove one or both testicles. Also called orchiectomy.

orchiectomy (or-kee-EK-toe-mee)

Surgery to remove one or both testicles. Also called orchidectomy.

organ

A part of the body that performs a specific function. For example, the heart is an organ.

organism

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

oropharynx (or-o-FAIR-inks)

The part of the throat at the back of the mouth. It includes the soft palate, the base of the tongue, and the tonsils.

OSI-7904L

A substance that is being studied in the treatment of cancer. It belongs to the family of drugs called thymidylate synthase inhibitors.

osmolality

The concentration of particles dissolved in a fluid. The osmolality of serum can help diagnose several medical conditions such as dehydration, diabetes, and shock.

osmotic (ahz-MAH-tik)

Having to do with osmosis (the passage of a liquid through a membrane from a less concentrated solution to a more concentrated solution). This makes the concentrations in both solutions more equal.

osteitis deformans

A chronic condition in which both the breakdown and regrowth of bone are increased. Osteitis deformans occurs most frequently in the pelvic and leg bones, skull, and lower spine. It is most common in older individuals, and may lead to bone pain, deformities, and fractures. Also called Paget's disease of bone.

osteogenic sarcoma

A cancer of the bone that usually affects the large bones of the arm or leg. It occurs most commonly in young people and affects more males than females. 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 usually affects the large bones of the arm or leg. It occurs most commonly in young people and affects more males than females. 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.

OTC

Over-the-counter. A medicine that can be bought without a prescription (doctor's order). Examples include analgesics (pain relievers) such as aspirin and acetaminophen. Also called nonprescription.

OTI-010

A preparation of laboratory-treated human mesenchymal stem cells that is being studied for its ability to prevent or decrease graft-versus-host disease in patients having stem cell transplants.

otolaryngologist (OAT-oh-LAR-in-GOL-uh-jist)

A doctor who specializes in treating diseases of the ear, nose, and throat. Also called an ENT (ear, nose, and throat) doctor.

ounce

A measure of weight (one-sixteenth pound) and volume (one-eighth cup).

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 cancer (oh-VAYR-ee-un KAN-ser)

Cancer that forms in tissues of the ovary. Most ovarian cancers are either ovarian epithelial carcinomas (cancer that begins in cells that line the ovary) or malignant germ cell tumors (cancer that begins in egg cells).

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.

ovary (O-va-ree)

One of a 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.

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.

overgrowth syndrome

A group of genetic disorders in which there is an abnormal increase in the size of the body or a body part that is often noted at birth. Examples of overgrowth syndromes include neurofibromatosis, Sotos syndrome, Beckwith-Wiedemann syndrome, Simpson-Golabi-Behmel syndrome, Weaver syndrome, Proteus syndrome, Sturge-Weber syndrome, and fragile X syndrome. Many of these syndromes increase the risk of cancer.

over-the-counter

OTC. A medicine that can be bought without a prescription (doctor's order). Examples include analgesics (pain relievers) such as aspirin and acetaminophen. Also called nonprescription.

overweight

Being too heavy for one's height. Excess body weight can come from fat, muscle, bone, and/or water retention. Being overweight does not always mean being obese.

ovulation (ov-yoo-LA-shun)

The release of an egg from an ovary during the menstrual cycle.

oxaliplatin

A drug that is used to treat colorectal cancer, and is being studied in the treatment of other types of cancer. It belongs to the family of drugs called platinum compounds. Also called Eloxatin.

oxandrolone (ox-AN-dro-lone)

A drug used to help patients gain weight after injury, chronic infection, or severe illness. It belongs to the family of drugs called anabolic steroids.

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.