The term AML M1 or M2 relates to the French-American-British (FAB) groups classification of Acute Leukemia's and Myelodysplastic Syndromes. The FAB classification was developed in the 1970’s firstly as an aid to differentiate Acute Lymphoid from Acute Myeloid Leukemia, classification is based solely on the cytochemical morphology of cells to elucidate their lineage and maturation. In the 1980’s further development of the FAB classification sub divided the Acute Myeloid Leukemia's into 8 categories based upon the morphological features of the cells:-

M0 – AML with minimal evidence of differentiation

M1 – Poorly differentiated no Myeloid maturation

M2 – Myeloblastic with some Myeloid maturation

M3 and M3v – Promyelocytic Leukemia

M4 – Acute Myelomonocytic leukemia

M5a and M5b  – Monoblastic Leukemia

M6 – Erythroblastic Leukemia

M7 – Megakaryoblastic Leukemia

With the development of techniques such as cytogenetics and immunophenotyping the World Health Organization (WHO) proposed a new classification which was based on the genetic, immunophenotypic, biological and clinical features of patients to better define specific disease entities.

The WHO classification of AML (briefly)

AML with myelodysplastic syndrome, therapy related

AML with recurrent genetic abnormalitiese.g. AML with t(8;21)(q22;q22), AML1(CBFA)-ETO fusion gene, Acute Promyelocytic Leukemia (AML with t(15;17)(q22;q11-12) and PML-RARA fusion gene or variants with RARA .

AML with multilineage myelodysplasia

AML Not Otherwise Categorized.in such cases the FAB classification is used.