Cancer (medicine), any of more than 100 diseases characterized by excessive, uncontrolled growth of abnormal cells, which invade and destroy other tissues. Cancer develops in almost any organ or tissue of the body, but certain types of cancer are more lethal than others. Cancer is the leading cause of death in Canada and second only to heart disease in the United States.
Evading the many obstacles that guard against runaway cell division is still not enough for cancer to develop. A malfunctioning cell must also skirt a number of safety mechanisms designed to prevent cells from growing where they are not supposed to in the body.
Normal cells adhere to each other and to a fibrous meshwork called an extracellular matrix. This matrix exists throughout all tissues and provides the structural support on which cells grow and form organs and other complex tissues. While a normal cell will often die if it cannot adhere to an extracellular matrix, cancer cells survive without this matrix.
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