Cells divide and increase their number in a process called mitosis. Normal cells divide to replace those lost, or to repair injuries. Cancer is an abnormal, continuous multiplying of cells. The cells divide uncontrollably and may grow into nearby tissue or spread to others parts of the body. This mass of cells eventually become large enough to produce lumps, masses, or tumors. These masses can be benign or malignant. Benign tumors are not cancerous, can usually be removed, often do not come back and in most cases do not spread to other parts of the body or invade other tissues. Malignant tumors are cancerous, can invade and damage nearby tissues and organs, they metastasize (break away from a malignant tumor and enter the bloodstream or lymphatic system forming secondary tumors in other parts of the body).
There are many types of cancer, including: