What Determines a Type of AML?
All blood cells, including red blood cells, platelets, and white blood cells, begin as a single stem cell in the bone marrow. Stem cells themselves do not have the ability to form clots, carry oxygen, or fight infection, but they develop or mature into fully functional blood cells that do.
Stem cells grow into immature blood cells, which look and act a little more like the “adult” cell they will eventually become with each stage of development they go through. Once the blood cell is mature enough to carry out its role in the body, it is released from the bone marrow and into the bloodstream, where it will remain for the rest of its life.
In the case of acute leukemia, there is an overproduction and release of very immature blood cells. The leukemia cells become “stuck” at one stage of development, and remain unable to do the function they are designed to do.
Types are determined by what stage of development the cells stop at.
There are two classification systems for identifying AML subtypes – the French-American-British (FAB) system and the World Health Organization (WHO) classification system.
The FAB is the one most commonly used. To classify AML using this system, doctors will look at the leukemia cells they obtain during the bone marrow biopsy. Beyond determining what stage of development the cells are at, they will also determine what kind of cell they were supposed to become when mature.
The chart below explains this system in greater detail.
Why Does My AML Subtype Matter?
Your AML subtype helps doctors to predict treatment, outcomes, prognosis, and behavior of your disease.
For example, in a study published in 2015, researchers found that types M4, M5, M6, and M7 had the lowest survival rates. M4 and M5 subtype leukemia cells also are more likely to form masses called granulocytic sarcomas (lesions that form in soft tissue or bone) and to spread to the cerebrospinal fluid (CSF).
Treatment is the same for most subtypes of acute leukemia with the exception of APL (M3). Different medications are used to treat APL, and the prognosis tends to be better than with other types of acute leukemia.
The FAB Classification System
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