Cancer definition: A diseases in which abnormal cells divide without control and can invade nearby tissues. Cancer cells can also spread to other parts of the body through the blood and lymph systems.

There are several main types of cancer;

  1. Carcinoma is a cancer that begins in the tissues that line or cover internal organs.
  2. Leukemia is a cancer that starts in blood-forming tissue such as the bone marrow, and causes large numbers of abnormal blood cells to be produced and enter the blood.
  3. Multiple myeloma and lymphoma are cancers that begin in the cells of the immune system.
  4. Sarcoma is a cancer that begins in bone, cartilage, blood vessels, muscle, fat or other supportive or connective tissue.

Here is a simple video by khanacademy.org talks about cancer definition and how it developed.