Leukemia is a cancer that starts in blood stem cells (immature blood cells) in the bone marrow. Bone marrow is the soft, spongy material that fills the centre of most bones. Blood cells are made in the bone marrow. Blood stem cells develop into either myeloid stem cells or lymphoid stem cells.
Myeloid stem cells develop into red blood cells, white blood cells or platelets.
- Red blood cells carry oxygen to all tissues of the body.
- There are many different types of white blood cells. Myeloid stem cells can develop into granulocytes and monocytes, which destroy bacteria and help to fight infection.
- Platelets form clots in damaged blood vessels to prevent bleeding.
Lymphoid stem cells develop into lymphocytes. Lymphocytes are another type of white blood cell. They are usually found in the blood and different parts of the lymphatic system, such as the lymph nodes and the spleen. Lymphocytes make antibodies to help fight infection.
Leukemia develops when the blood stem cells in the bone marrow make abnormal blood cells. These abnormal cells are called leukemia cells. Over time, the leukemia cells crowd out normal blood cells. This makes it hard for the white blood cells, red blood cells and platelets to do their jobs.
Types of leukemia
There are several different types of leukemia. The types of leukemia are first grouped based on the type of blood stem cell they developed from:
- Myelogenous leukemias develop from abnormal myeloid cells.
- Lymphocytic leukemias (also known as lymphoblastic leukemias) develop from abnormal lymphoid cells.
The types of leukemia are further grouped based on how quickly the leukemia develops and grows:
- Acute leukemias start suddenly, developing within days or weeks. The number of leukemia cells in the blood can rise very fast and blood cells cannot do their jobs.
- Chronic leukemias develop slowly over months or years. They may not cause any symptoms early in the disease. Symptoms start to appear as the number of leukemia cells in the blood or bone marrow increases.
The 4 main types of leukemia are:
Each type of leukemia is treated differently because it develops and grows differently. Your doctor will find out which type of leukemia you have to make sure you get the treatment that works best for that type.