Words to Know


Having a higher-than-ideal amount of body fat. Obesity is generally determined by a body mass index (BMI) calculation that defines whether and individual is underweight, at a healthy weight, overweight, or obese based on the person's height and weight. A BMI of 18.5 to 24.9 is considered healthy, and a BMI of greater than 30 is considered obese. Experts concluded in 2001 that several cancers are associated with obesity, including postmenopausal breast cancer.

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). In contrast, a 'subjective' improvement is based on how one person perceives her own health, or someone else's health.

objective response

A measurable response. In contrast, a 'subjective' response is based on how one person perceives her own health, or someone else's health.


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

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).


Blockage of a passageway.


Describes the legal use of a prescription medicine to treat a disease or condition when the agent has not yet been approved for that use by the U.S. Food and Drug Administration.


Olaparib is a type of targeted therapy agent called a poly (ADP-ribose) polymerase (PARP) inhibitor. It is being studied in the treatment of breast cancer, as well as ovarian and cancer caused by mutations (changes) in the BRCA1 and BRCA2 genes. It is also being studied in the treatment of other types of cancer. It blocks an enzyme involved in many functions of the cell, including the repair of DNA damage, and it may kill cancer cells. DNA damage may be caused by normal cell actions, UV light, some anticancer agents, as well as radiation used to treat cancer. Also called AZD2281 and PARP inhibitor AZD2281.


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.


The study of cancer.

oncology nurse

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

oncology pharmacy specialist

Also called BCOP and board certified oncology pharmacy specialist. A licensed pharmacist with special training in how to design, give, monitor, and change chemotherapy for individuals being treated for cancer.


The lysis (breakdown) of cancer cells. This can be caused by chemical or physical means (for example, strong detergents or high-energy sound waves) or by infection with a strain of virus that can lyse cells.


The active ingredient in a medicine used to treat nausea and vomiting caused by cancer treatment. Ondansetron is a type of serotonin receptor antagonist and a type of antiemetic.

onset of action

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


Surgery to remove one or both ovaries. Women at high risk for breast cancer are, such as those with the BRCA1 (breast cancer 1) and BRCA2 (breast cancer 2) genes, are sometimes advised to undergo oophorectomy. This surgery can reduce the risk of both breast and ovarian cancers. BRCA gene carriers are at a much higher risk for breast and ovarian cancers than the average person.

open biopsy

A lumpectomy to remove a breast tumor is a type of open biopsy. Open biopsy is 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.

open label study

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

open resection

Surgery to remove part or all of an organ or a tumor and nearby lymph nodes. The incision is large enough to let the surgeon see into the body.


Describes a condition that can be treated by surgery.