Acute myelogenous leukemia stages
Because AML starts in the bone marrow and is usually not detected until it has spread to other organs, traditional cancer staging is not needed. Rather than using the common TNM method for evaluating the cancer, the subtype of AML is classified using a cytologic (cellular) system. Physicians are better able to predict how the cancer will respond to treatment based on the cellular classification and, in turn, more accurately assess the prognosis (outlook).
AML subtypes and staging
Using a system known as French-American-British (FAB) classification, AML is classified in eight subtypes, M0 through M7, based on:
- The number of healthy blood cells
- The size and number of leukemia cells
- The changes that appear in the chromosomes of the leukemia cells
- Any other genetic abnormalities that have occurred
The eight acute myelogenous leukemia stages are classified as follows:
- Undifferentiated AML - M0: In this stage of acute myelogenous leukemia, the bone marrow cells show no significant signs of differentiation.
- Myeloblastic leukemia - M1: Bone marrow cells show some signs of granulocytic differentiation with or without minimal cell maturation.
- Myeloblastic leukemia - M2: Maturation of the bone marrow cells is beyond the promyelocyte (early granulocyte) stage. Varying amounts of granulocyte maturation may be observed.
- Promyelocytic leukemia - M3: Most of the abnormal cells are early granulocytes, between myeloblasts and myelocytes in their stage of development. The cells contain many small particles and have nucleuses of varying size and shape.
- Myelomonocytic leukemia - M4: In this stage of acute myelogenous leukemia, the bone marrow and circulating blood have variable amounts of monocytes and differentiated granulocytes in them. The percentage of monocytes and promonocytes in the bone marrow is greater than 20 percent. There may also be an increased number of granular leukocytes called eosinophils, a type of granulocyte that often has a two-lobed nucleus.
- Monocytic leukemia - M5: This subset is further divided into two different categories. The first is characterized by poorly differentiated monoblasts with lacy-appearing genetic material. The second subset is characterized by a large number of monoblasts, promonocytes and monocytes. The proportion of monocytes in the bloodstream may be higher than that in the bone marrow.
- Erythroleukemia - M6: This form of leukemia is characterized by abnormal red blood cell-forming cells, which make up over half of the nucleated cells in the bone marrow.
- Megakaryoblastic leukemia - M7: The blast cells in this form of leukemia look like immature megakaryocytes (giant cells of the bone marrow) or lymphoblasts (lymphocyte-forming cells). M7 leukemia may be distinguished by extensive fibrous tissue deposits (fibrosis) in the bone marrow.
Although the FAB classification is still commonly used to group AML into subtypes, the World Health Organization (WHO) has proposed a new acute myelogenous leukemia staging system in an attempt to more clearly communicate the patient's prognosis (outlook). This system divides AML into broad groups:
- Acute myelogenous leukemia with certain genetic abnormalities: Cellular testing is capable of identifying specific genetic abnormalities:
- AML with a translocation between chromosomes 8 and 21
- AML with a translocation or inversion in chromosome 16
- AML with changes in chromosome 11
- APL (M3), which usually has translocation between chromosomes 15 and 17
- AML with multi-lineage dysplasia: More than one type of abnormal myeloid cell is involved.
- AML from previous chemotherapy/radiation
- AML not otherwise specified: This includes AML cases that don't fall into any of the above groups, such as:
- Undifferentiated AML - M0
- AML with Minimal Maturation - M1
- AML with Maturation - M2
- Acute Myelomonocytic Leukemia - M4
- Acute Monocytic Leukemia - M5
- Acute Erythroid Leukemia - M6
- Acute Megakaryoblastic Leukemia - M7
- Acute Basophilic Leukemia
- Acute Panmyelosis with Fibrosi
- Myeloid Sarcoma - Also called Granulocytic Sarcoma or Chloroma
- Undifferentiated/biphenotypic acute leukemias: This type of leukemia may exhibit features of both lymphocytic and myelogenous leukemia. This may also be referred to as ALL with myeloid markers, AML with lymphoid markers or mixed lineage leukemia.