Magnetic resonance (MR or MRI) imaging: A method of obtaining cross-sectional images of the inside of the body. Instead of using x-rays, MRI uses a powerful magnet and transmits radio waves through the body; the images appear on a computer screen as well as on film. Like x-rays, the procedure is physically painless, but some people find it psychologically uncomfortable to spend 30 minutes or more in the small core of the MRI machine. Also called nuclear magnetic resonance (NMR).

Magnification mammography views: Uses a small magnification table to bring the breast closer to the x-ray source and further away from the film plate. This allows the acquisition of "zoomed in" images (2 times magnification) of the region of interest. Magnification views provide a clearer assessment of the borders and the tissue structures of a suspicious breast area or a mass and are often used to evaluate microcalcifications.

Malignancy: Term used to describe a mass of cancer cells. Malignant tumors may invade surrounding tissues or spread (metastasize) to distant areas of the body. See cancer.

Mammastatin: A protein that is being studied in connection with breast cancer prediction and treatment. Mammastatin is thought to be a naturally occurring protein produced by breast cancer cells. The protein was first identified in 1986 and has been determined in preliminary research to be lacking in the majority of breast cancer patients and healthy women who have a family history of breast cancer.

Mammoplasty: Plastic surgery to reconstruct the breast or to change the shape, size, or position of the breast. Reduction mammoplasty reduces the size of the breast(s). Augmentation mammoplasty enlarges the size of the breast(s), usually with implants.

Mammogram, mammography: An x-ray of the breast; used to screen for or investigate breast abnormalities and breast cancer, particularly those which are too small to be felt by physical examination. Mammograms are made using a special x-ray machine designed specifically for this purpose. Screening mammography is used for early detection of breast cancer in women without any breast symptoms. Diagnostic mammography is used to help characterize suspicious breast masses or determine the cause of other breast symptoms.    

Mass: Any group of cells clustered together more densely than the surrounding breast tissue. Masses can be palpable (able to be felt) or nonpalpable (unable to be felt).  Masses can be benign or malignant.

Mastalgia: Cyclic or non-cyclic pain in the breast or in the axilla (underarm) region of the body.   Approximately 15% of women with breast pain require treatment.  Breast pain is not usually (but can be) associated with breast cancer.

Mastectomy: Surgery to remove all or part of the breast and sometimes other tissue. Extended radical mastectomy removes the breast, skin, nipple, areola, chest muscles (pectoral major and minor), and all axillary and internal mammary lymph nodes on the same side. Halsted radical mastectomy removes the breast, skin, nipple, areola, both pectoral muscles, and all axillary lymph nodes on the same side. Modified radical mastectomy removes the breast, skin, nipple, areola, and most of the axillary lymph nodes on the same side, leaving the chest muscles intact. Partial mastectomy removes less than the whole breast, taking only part of the breast in which the cancer occurs and a margin of healthy breast tissue surrounding the tumor. Subcutaneous mastectomy is surgery to remove internal breast tissue. The nipple and skin are left intact. Prophylactic mastectomy is a mastectomy done before any evidence of cancer can be found, for the purpose of preventing cancer. This procedure is sometimes performed on women at very high risk of breast cancer. Quadrantectomy is a partial mastectomy in which the quarter of the breast that contains a tumor is removed. Segmental mastectomy is a partial mastectomy. Simple mastectomy or total mastectomy removes only the breast and areola.

Mastitis: Inflammation or infection of the breast.

Mastopexy: Surgery to lift sagging breasts.  The procedure is not permanent.

Medical oncologist: See oncologist.

Medullary carcinoma: A special type of infiltrating ductal carcinoma with especially sharp boundaries between tumor tissue and normal tissue. About 5% of breast cancers are medullary carcinomas. The outlook (prognosis) for this kind of cancer is considered to be better than average.

Menarche: A woman’s first menstrual period. Early menarche (before age 12) is a risk factor for breast cancer, possibly because the earlier a woman’s periods begin, the longer her exposure to estrogen.

Menopause: The time in a woman's life when monthly cycles of menstruation cease forever and the level of hormones produced by the ovaries decreases. Menopause usually occurs in the late 40s or early 50s, but it can also be caused by surgical removal of both ovaries (oophorectomy), or by some chemotherapies that destroy ovarian function. (See also estrogen replacement therapy).

Menstruation: The periodic shedding of the uterine lining (the endometrium) accompanied by bleeding; occurring approximately monthly from puberty to menopause in non-pregnant women.

Metachronous: At different times. (See also bilateral).

Metastasis: The spread of cancer cells to distant areas of the body by way of the lymph system or bloodstream.  25% of metastatic breast cancer spreads first to the bone.  

Metastatic breast cancer: Cancer cells that have spread past the breast and the axillary lymph nodes to distant regions of the body (such as the bone, liver, lung, or brain). 

Microcalcifications: See calcifications.   

Micrometastases: The spread of cancer cells in groups so small that they can only be seen under a microscope.

Microvascular flap: A surgical technique that reattaches the small vessels of the flap to the small recipient site vessels.  See also “free” flap.

Modified radical mastectomy: See mastectomy.

Monoclonal antibodies: Antibodies manufactured in the laboratory and designed to seek out as targets specific substances recognized by the immune system (antigens). Monoclonal antibodies which have been attached to chemotherapy drugs or radioactive substances are being studied for their potential to seek out antigens unique to cancer cells and deliver these treatments directly to the cancer, thus killing the cancer cell and not harming healthy tissue. Monoclonal antibodies are often used in immunocytochemistry to help detect and classify cancer cells. Other studies are being done to see if radioactive atoms attached to monoclonal antibodies can be used in imaging tests to detect and locate small groups of cancer cells. (See also antibody, antigen, immunocytochemistry).

Monomorphic: Of the same shape. Monomorphic often describes microcalcifications that are uniform in shape and density (and usually non-cancerous).

Mucinous carcinoma: A tumor that is sticky because of a large amount of mucin released by its cells. Mucin is a carbohydrate that is the main component of mucus. 

Multicentric breast cancer: Breast cancer occurring in multiple areas of a breast.

Multiform: Having an irregular shape or various shapes. Term often used to describe microcalcifications, which can indicate ductal carcinoma in situ (DCIS), an early stage breast cancer.

Myocutaneous flap: A flap of tissue that consists of skin, fatty and muscle tissue from a place in the body (such as the abdomen) that is used to reconstruct the breast.

Updated: August 2006