Cancer

Cancer, known scientifically as a Malignant neoplasm, is a disease in which affected cells can display three of the following properties:
 * Uncontrollable cellular reproduction above normal rates (this forms a Malignant tumor);
 * Invasion and destruction of neighboring tissue; and sometimes
 * Metastasis, a state in which affected cells spread throughout the body through the blood.

Halo Universe
Cancer ceased to be commonplace in the Human genome by the 22nd century, though cases appeared from time to time as far as the 26th century. These could be treated easily, by this time however.

At some time during the Human-Covenant War, Michael Baird was diagnosed with this disease onboard the.