Macule: A small, flat, distinct colored area of skin that is less than 10 millimeters in diameter, and does not include a change in skin texture or thickness.

Malignant: Cancerous; cells that can invade and destroy nearby tissue and spread to other parts of the body.

Medical oncologist: See oncologist.

Melanin: A dark-brown to black pigment found in the skin, hair, and parts of the eyes.

Melanocytes: Pigment-producing cells located in the epidermis.

Melanoma: A highly malignant type of skin cancer that arises in melanocytes, the cells that produce pigment. Melanoma usually begins in a mole.

Metastasis: The spread of cancer cells from their point of origin to other parts of the body by way of the bloodstream or the lymphatic system.

Metastatic melanoma: Melanoma that has spread to other parts of the body by way of the bloodstream or the lymphatic system.

Mole: A cluster of melanocytes and surrounding supportive tissue that usually appears as a tan, brown, or flesh-colored spot on the skin. Also called a nevus.

MRI: Magnetic Resonance Imaging. A radiology technique using magnetism, radio waves, and a computer to enhance internal images of the body.

Mutation: A permanent change in the structure of a cell that may cause it to become cancerous.

Myalgia: Muscle pain.