Cancer

Cancer is a group of diseases characterized by uncontrolled growth of tissue cells in the body and the invasion by these cells into nearby tissue and migration to distant sites. Cells are the building blocks of living things.
Cancer grows out of normal cells in the body. Normal cells multiply when the body needs them, and die when the body doesn't need them. Cancer appears to occur when the growth of cells in the body is out of control and cells divide too quickly. It can also occur when cells forget how to die.
There are many different kinds of cancers. Cancer can develop in almost any organ or tissue, such as the lung, colon, breast, skin, bones, or nerve tissue.

Leukemia

Leukemia is cancer of the blood cells. It starts in the bone marrow, the soft tissue inside most bones. Bone marrow is where blood cells are made.
When you are healthy, your bone marrow makes:
1. White blood cells, which help your body fight infection.
2. Red blood cells, which carry oxygen to all parts of your body.
3. Platelets, which help your blood clot.
When you have leukemia, the bone marrow starts to make a lot of abnormal white blood cells, called leukemia cells. They don't do the work of normal white blood cells, they grow faster than normal cells, and they don't stop growing when they should.