Magnetic Resonance Imaging (MRI): A diagnostic procedure which uses magnetic fields instead of radiation to produce images of the body.

Maintenance Therapy: Chemotherapy medicine given to prolong a remission.

Malignant: Cancerous.

Malignant Tumor: A tumor containing cancer cells that can spread to other organs and parts of the body.

Margins: The area of normal tissue surrounding a cancer that has been removed. "Clean margins" means no cancer cells are present in the normal tissue around the cancer and, therefore, there is little chance cancer has been left behind.

Marrow Donation: A surgical procedure by which a person donates a portion of their bone marrow for a patient who had diseased marrow and needs a marrow transplant.

Match: In stem cell transplantation, the word "match" relates to how similar the HLA tissue typing is between a donor and a recipient. When a donor and a recipient’s HLA A, B and DR typing is the same they are said to be an "identical match", a "6 of 6" or a "perfect match."

MDS: See Myelodysplastic Syndromes

Mediastinum: The area between the lungs. The organs in this area include the heart and its large veins and arteries, the trachea, the esophagus, the bronchi, and lymph nodes.

Medulloblastoma: A type of brain tumor that research suggests develops from developing (primitive) nerve cells that normally do not remain in the body after birth. They are almost always found in children or young adults.

Melanoma: A very aggressive form of skin cancer associated with sun exposure.

Metastasis: The spread of cancer cells from the original site to other areas of the body.

Molecular Typing: Molecular typing is a term used interchangeably with DNA-based typing or genotyping.

Monocyte: A type of white blood cell. It has a single well-defined nucleus and consumes large foreign particles including bacteria and cell debris.

Morbidity: A term that usually refers to the suffering or misery that people experience who have an illness or are under treatment for an illness.

Mortality: The number of deaths that occur in a given time, in a given group, or from a given cause.

MRI: See Magnetic Resonance Imaging

Mucositis: Inflammation of the lining of the mouth, the throat, the gastrointestinal tract, the genital or urinary tracts.

Multiple Myeloma: A form of cancer of the bone marrow. It affects the plasma cells that produce antibodies and can be diagnosed by the presence of abnormal proteins or antibodies in the blood. Multiple myeloma is frequently associated with bone pain and susceptibility to infection.

Myeloblast (Myeloblastic): Immature non-lymphocyte type white blood cells. It is normally seen only in the bone marrow. In some diseases, such as leukemia, myeloblasts may appear in the blood. Healthy myeloblasts will develop into granulocytes.

Myelodysplastic Syndromes (MDS): Also called pre-leukemia. A group of disorders in which the bone marrow does not function normally and not enough normal blood cells are made.

Myelofibrosis: A progressive disease in which the cells of the bone marrow that produce scarring rather than blood cells begin to multiply rapidly. This leads to anemia and enlargement of the spleen and liver. Myelofibrosis can occur as part of a myeloproliferative disorder, or as a result of another unrelated condition.

Myeloid: A term referring to myelocytes, a type of white blood cell. Also called myelogenous.

Myeloma: Also called multiple myeloma. A malignant tumor of the plasma cell, which is produced in the bone marrow, and associated with the production of abnormal proteins or antibodies.

Myeloproliferative Disorder: The Myeloproliferative Disorders are diseases where too many of some types of blood cells are made in the bone marrow. The four major types of myeloproliferative disorders are chronic myelogenous leukemia, essential thrombocytopenia, idiopathic myelofibrosis, and polycythemia vera.

Myelosuppression: A decrease in the production of red blood cells, platelets and some white blood cells by the bone marrow.