Archived Tumor Sample: A tumor sample that has been routinely preserved and stored. Tumor tissue is commonly preserved for storage by being treated with a preservative called formalin and then embedded in paraffin (wax).

Aromatase Inhibitor: A medication that reduces the amount of estrogen in the body. Aromatase inhibitors may be used to treat women with estrogen receptor-positive breast cancer.

Biopsy: A procedure where tumor tissue is removed from the body for laboratory examination to determine whether or not cancer is present. A biopsy can be performed using a needle to extract a small piece of tissue or as a surgical procedure to remove a larger piece of tissue.

BRCA1 and BRCA2: Genes that normally help control cell growth. A person who inherits an altered version of the BRCA1 and/or BRCA2 genes has a higher risk of getting breast and ovarian cancer.

Cancer: A condition in which abnormal cells divide without control. Cancer cells can also invade nearby tissues and can spread through the bloodstream and lymphatic system to other parts of the body.

Chemotherapy: Treatment with cytotoxic drugs that destroy cancer cells (fast-growing cells). Chemotherapy may be used in addition to surgery and is sometimes used in combination with other therapies such as radiation therapy or hormonal therapy.

Clinical Trial: A research study to test drugs, procedures, or testing technologies to determine whether these are effective and/or safe.

Core Biopsy: A procedure which uses a needle to remove a small, intact sample of tissue from an identified breast mass in order to examine it and obtain a preliminary diagnosis.

Diagnosis: Identification of a condition, such as breast cancer, by its signs and symptoms, and the results of laboratory tests or other examinations.

Distant Recurrence: The spread of cancer to parts of the body other than the place where the cancer first occurred.

Early-Stage Breast Cancer: A term that can be used to describe Stage I and II, lymph node-negative breast cancer.

ER (Estrogen Receptor): A feature (protein) that may be present on certain cells to which estrogen molecules can attach. The term "ER positive" refers to tumor cells that contain the estrogen-receptor protein. These cells are generally sensitive to hormone therapy.

Gene: The functional and physical units of inheritance that are passed from parents to their offspring. The genes found in normal breast tissue can change their "expression" (see below), which can give rise to breast cancer.

Gene Expression: The level of activity of a gene or group of genes.

Gene Expression Profile: A picture of the activity or expression of multiple genes from a single specimen.

Genetics: The study of genes and heredity. Heredity is the passing of genetic information and traits (such as eye color and an increased chance of getting a certain disease) from parents to offspring.

Genome: The complete genetic material of a living thing.

Genomics: The study of complex sets of genes and their effects on biology.

Hormonal Therapy: Medications used to reduce the effect of hormones in the body. In many cases of breast cancer, hormones can fuel the growth of breast cancer. Common hormonal therapies include tamoxifen and a newer class of drugs called aromatase inhibitors. Hormonal therapies are used to treat women with estrogen receptor-positive breast cancer.

Hormone Receptor: A protein on the surface of a tumor cell that binds to a certain hormone, activating tumor growth.

Human Genome Project: An international research and technology-development effort aimed at mapping and sequencing the entire genome of human beings.

In Situ (carcinoma in situ): Non-invasive cancer in which abnormal cells are isolated within the lobes or milk ducts of the breast and have not spread to nearby tissue.

Invasive Breast Cancer: Cancer that has spread from where it started in the breast into surrounding, healthy tissue. Most invasive breast cancers start in the ducts (tubes that carry milk from the lobules to the nipple). Invasive breast cancer can spread to other parts of the body through the blood and lymph systems. Invasive breast cancer is also called infiltrating breast cancer.

Local Recurrence: The reappearance of cancer in the part of the body where it first occurred.

Lumpectomy: A surgical procedure that removes a localized mass of tissue, including the breast cancer tumor and a small amount of normal, non-cancerous tissue surrounding the tumor.

Mastectomy: A surgical procedure to remove all or a large part of the breast.

Metastatic Breast Cancer: Breast cancer that has spread beyond the breast and local lymph nodes to other parts of the body.

Newly Diagnosed: A term used to describe breast cancer that has recently been identified.

Node-Negative Breast Cancer: Breast cancer that has not spread to the lymph nodes.

Node-Positive Breast Cancer: Breast cancer that has spread to the lymph nodes (most commonly the axillary lymph nodes under the arms).

Oncotype DX^®: A unique diagnostic test that looks at the genomic profile of a breast tumor to quantify the likelihood that early-stage, estrogen receptor-positive, lymph node-negative breast cancer will return, or recur (distant recurrence), and provide information about a woman's likely benefit from chemotherapy (commonly used drugs to treat early-stage breast cancer). A recent study has also shown that Oncotype DX may be informative for newly diagnosed women who are post-menopausal and have node-positive, hormone receptor-positive breast cancer.

Pathology Report: A report ordered by authorized healthcare professionals that describes what was found in tissue removed from the body after the tumor and surrounding tissue are checked by a pathologist. Usually includes information on tumor grade and stage.

PR (Progesterone Receptor): A feature (protein) that may be present on certain cells to which progesterone molecules can attach. The term "PR positive" refers to tumor cells that contain the progesterone receptor protein. These cells are generally sensitive to hormone therapy.

Radiation Therapy: The use of radiation to destroy cancer cells. Radiation therapy may be used before or after surgery, and is sometimes used in combination with chemotherapy. Radiation is used for local control of the cancer at the site of the tumor.

Recurrence: A return of cancer after treatment. This can be either local (at the site of the original tumor), or distant (beyond the original site).

Screening: Looking for masses or suspicious areas in breast tissue on a periodic basis.

Staging: A classification system for breast cancer based on the size of the tumor, whether the cancer has spread to the lymph nodes, and whether the cancer has spread to other sites in the body (metastasis).

Stage I Breast Cancer: The tumor is up to 2 centimeters in diameter and has not spread beyond the breast.

Stage IIA Breast Cancer: The tumor is up to 2 centimeters and has spread to the axillary lymph nodes under the arm, or the tumor is between 2 and 5 centimeters and has not spread to the lymph nodes.

Stage IIB Breast Cancer: The tumor is between 2 and 5 centimeters and has spread to the lymph nodes under the arm, or the tumor is larger than 5 centimeters in diameter and has not spread to the lymph nodes.

Stage IIIA Breast Cancer: The tumor is larger than 5 centimeters in diameter and has spread to the lymph nodes under the arm, or the tumor is any size and has spread more extensively in the lymph nodes.

Stage IIIB Breast Cancer: The tumor is any size and has extended to other tissues near the breast; the tumor may or may not have spread to the lymph nodes.

Stage IV Breast Cancer: Cancer that has spread to other locations in the body (metastasized).

Surveillance/Follow-Up: An ongoing assessment by the medical team, once treatment has been completed, to assess the cancer's remission and to look for any evidence of a cancer’s return.

Tamoxifen: A medication that interferes with the activity of the hormone estrogen. Tamoxifen is used to treat women with estrogen receptor-positive breast cancer.

Treatment Monitoring: An ongoing and frequent assessment by the medical team, during the time of treatment, to monitor how the patient is tolerating the treatment and how the cancer is responding.

Tumor: Tissue growth where the cells that make up the tissue have multiplied uncontrollably. A tumor can be benign (non-cancerous) or malignant (cancerous).

Tumor Grade: The characterization of a tumor based on how similar in appearance the cancer cells are to normal cells, and on how many of those tumor cells are dividing. Tumor grade is one of many factors that, when used in combination, can indicate how aggressive someone's cancer is.

Tumor Stage: The status of cancer based on the size of the tumor, whether it has spread to the lymph nodes, and whether it has spread to other sites in the body (metastasis).