What Is Acute Myeloid Leukemia?
Leukemias are cancers that start in cells that would normally develop
into different types of blood cells.
Acute myeloid leukemia (AML) has many other names, including acute
myelocytic leukemia, acute myelogenous leukemia, acute granulocytic
leukemia, and acute non-lymphocytic leukemia.
“Acute” means that this leukemia can progress quickly if not treated,
and would probably be fatal in a few months. “Myeloid” refers to the
type of cell this leukemia starts from.
Most cases of AML develop from cells that would turn into white blood
cells (other than lymphocytes), but some cases of AML develop in other
types of blood-forming cells.
AML starts in the bone marrow (the soft inner part of certain bones,
where new blood cells are made), but in most cases it quickly moves into
the blood. It can sometimes spread to other parts of the body including
the lymph nodes, liver, spleen, central nervous system (brain and
spinal cord), and testicles.
Normal bone marrow, blood, and lymphoid tissue
To understand the different types of leukemia, it helps to know about the blood and lymph systems.
Bone marrow
Bone marrow is the soft inner part of some bones such as the skull,
shoulder blades, ribs, pelvic (hip) bones, and backbones. The bone
marrow is made up of a small number of blood stem cells, more mature
blood-forming cells, fat cells, and supporting tissues that help cells
grow.
Inside the bone marrow, blood stem cells develop into new blood
cells. During this process, the cells become either lymphocytes (a kind
of white blood cell) or other blood-forming cells, which are types of myeloid cells. These other blood-forming cells can develop into red blood cells, white blood cells (other than lymphocytes), or platelets.
Types of blood cells
Red blood cells carry oxygen from the lungs to all other
tissues in the body, and take carbon dioxide back to the lungs to be
removed. Having too few red blood cells in the body (called anemia) can make you feel tired, weak, and short of breath because your body tissues are not getting enough oxygen.
Platelets are actually cell fragments made by a type of bone marrow cell called the megakaryocyte.
Platelets are important in stopping bleeding. They help plug up holes
in blood vessels caused by cuts or bruises. Having too few platelets
(called thrombocytopenia) may cause you to bleed or bruise easily.
White blood cells help the body fight infections.
Having too few white blood cells weakens your immune system and can make
you more likely to get an infection.
Types of white blood cells
Lymphocytes are mature, infection-fighting cells that develop from lymphoblasts,
a type of blood stem cell in the bone marrow. Lymphocytes are the main
cells that make up lymphoid tissue, a major part of the immune system.
Lymphoid tissue is found in lymph nodes, the thymus (a small organ
behind the breast bone), the spleen, the tonsils and adenoids, and is
scattered throughout the digestive and respiratory systems and the bone
marrow. There are 2 main types of lymphocytes:
- B lymphocytes (B cells) protect the body from invading germs by developing (maturing) into plasma cells, which make proteins called antibodies. The antibodies attach to the germs (bacteria, viruses, and fungi), which helps other types of white blood cells recognize and destroy them.
- T lymphocytes (T cells) can recognize cells infected by viruses and directly destroy these cells. They also help regulate the immune response.
Granulocytes are mature, infection-fighting cells that develop from myeloblasts,
a type of blood-forming cell in the bone marrow. Granulocytes have
granules that show up as spots under the microscope. These granules
contain enzymes and other substances that can destroy germs, such as
bacteria. The 3 types of granulocytes – neutrophils, basophils, and eosinophils – are distinguished by the size and color of their granules.
Monocytes develop from blood-forming monoblasts in the
bone marrow and are related to granulocytes. After circulating in the
bloodstream for about a day, monocytes enter body tissues to become macrophages,
which can destroy some germs by surrounding and digesting them.
Macrophages also help lymphocytes recognize germs and make antibodies to
fight them.
Any of the blood-forming myeloid or lymphoid cells from bone marrow
can turn into a leukemia cell. Once this change takes place, the
leukemia cells no longer mature in a normal way. Leukemia cells often
reproduce quickly, but in most cases the problem is that they don’t die
when they should. They survive and build up in the bone marrow. Over
time, these cells spill into the bloodstream and spread to other organs,
where they can keep other cells in the body from doing their jobs.
Types of leukemia
Not all leukemias are the same. There are 4 main types of leukemia.
Knowing the specific type helps doctors better predict each patient’s
prognosis (outlook) and select the best treatment.
Acute Leukemia
The first factor in classifying a patient’s leukemia is whether most
of the abnormal cells look like normal white blood cells (mature) or
look more like stem cells (immature).
In acute leukemia, the leukemia cells are immature blood cells (called blasts).
These leukemias are fast growing because normal blast cells divide
quickly. But the leukemia cells don’t divide any more often than normal
blast cells do. They just don’t stop dividing when normal blast cells
would. Without treatment, most patients with acute leukemia would live
only a few months. Some types of acute leukemia respond well to
treatment, and many patients can be cured. Other types of acute leukemia
have a less favorable outlook.
Myeloid leukemia versus lymphocytic leukemia
The other main factor in classifying leukemia is the type of bone marrow cells that are affected.
Myeloid leukemias start in immature forms of myeloid cells –
white blood cells (other than lymphocytes), red blood cells, or
platelet-making cells (megakaryocytes). They are also known as myelocytic, myelogenous, or non-lymphocytic leukemias.
*This information is courtesy American Cancer Society. You can learn more HERE
