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# 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

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.

obese  
   An abnormally high, unhealthy amount of body fat.

objective improvement  
   An improvement that can be measured by the health care provider (for example, a decrease in pain can be measured by how much pain medicine the patient is taking).

objective response  
   A measurable response.

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.

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.

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.

OGX-011  
   A substance that is being studied as a treatment for cancer. It belongs to the family of drugs called antisense oligonucleotides.

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.

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.

opioid  
   A synthetic drug that is used to treat moderate to severe pain. Opioids are similar to opiates such as morphine and codeine.

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 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.

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.

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 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.

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.

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.

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

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.

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