magnetic resonance imaging (MRI) A diagnostic test that uses a combination of magnetism and radio waves to build up detailed cross-section pictures (or images) of part of a person's body. The test involves lying on a couch inside a metal cylinder (which forms a very large magnet) that is open at both ends. It may take up to one hour to complete, but is completely painless.

malignant Cancerous. Malignant cells can spread (metastasise) and can eventually cause death if they cannot be treated.

malignant tumour A tumour that is cancerous. A malignant tumour may invade and destroy surrounding tissues and can spread to other parts of the body: see benign.

mammary dysplasia [mam-ma-ry dys-pla-si-a] see benign fibrocystic changes.

mammography [mam-mog-ra-phy] A method of x-ray for early detection of breast cancer. Mammography may detect breast cancer before a lump can be felt. The x-ray itself is called a mammogram.

mastectomy [mas-tec-to-my] The surgical removal of a breast or part of a breast to treat breast cancer. Radical mastectomy is rarely done now. The operation most frequently performed is the modified radical mastectomy in which the entire breast and some lymph nodes in the armpit are removed, but no muscle. In subcutaneous mastectomy the breast tissue is removed but the skin and nipple are left, and can later be used to reconstruct the breast: see breast reconstruction.

medical imaging The use of a wide range of techniques to provide images of the inside of the body. In some hospitals, radiology and nuclear medicine are both part of a medical imaging department: see scan.

melanin The brown pigment which gives the skin its colour. Its role is to protect the body against the damaging effect of the ultraviolet rays present in sunlight and tanning machines in solariums.

melanocytes Cells in the epidermis and elsewhere that produce melanin.

melanoma [mel-a-no-ma] A very malignant form of skin cancer. Melanomas can occur anywhere on the body, including in the eye and the mucous membranes. A melanoma looks like a mole or freckle. It usually has an irregular outline and may vary in colour from black to almost white and in the early stages it is quite flat. The main symptom is a change in size, shape or colour over a period of weeks or months. A melanoma may start in an existing freckle or mole, but more often they start in normal-looking skin.

membrane A thin layer of tissue which covers a surface, lines a cavity or divides a space or organ.

meningioma [men-in-gi o-ma] A slow-growing tumour that arises in the meninges, the membranes that cover the brain and spinal cord. Some meningiomas are malignant : see brain tumour .

metastasis [me-ta-sta-sis] (pl. metastases) An extension of the primary tumour . It develops in a part of the body away from the original (primary) cancer . When cancer cells break away from the original tumour and are carried by the lymph and blood systems to other parts of the body they are said to metastasise. Even though the metastasis may be far away, it is not a new cancer: see cancer . Also known as secondary tumour or metastatic tumour.

metastasise [me-ta-sta-sise] see metastasis .

microcalcifications [mi-cro cal-ci fi-ca-tions] Tiny flecks of calcium that may be present in the breast that will show up on a mammogram. A cluster of microcalcifications suggests that breast cancer may be present.

milk duct/milk sac see breast .

mole A term that loosely describes any pigmented (coloured), fleshy growth on the skin .

Monilia [mon-il-i-a] Former name for the fungus now called Candida albicans.

morbidity Sickness, illness.

morphine A strong and effective painkiller which is used commonly to treat people with cancer who have pain.

MRI see magnetic resonance imaging .

mucositis [mu-co-si-tis] see stomatitis .

mutation A change in the genetic material of a cell . This may occur spontaneously or be caused by something outside the cell (a mutagen).

myeloid [my-e-loid] Of the bone marrow .

myeloma [my-e-lo-ma]A cancer that arises in plasma cells that are found in the bone marrow : see multiple myeloma