Acute myeloid leukaemia
Classification
The WHO system has now largely superseded the French-American-British (FAB) classification. The newer classification reduces the bone marrow leukaemic blast cell percentage differentiating AML from myelodysplastic syndrome (see p. 50) from 30% to 20%. Other key changes include the creation of specific subtypes with non-random cytogenetic or equivalent molecular abnormalities, and the distinction of patients with multilineage dysplasia and also previous chemotherapy. The major FAB subtypes are included in the ‘other’ category with the exception of acute promyelocytic leukaemia (previously FAB M3) which is now in the ‘recurrent translocations’ group due to the inevitable presence of t(15;17). It can be seen (Table 20.1) that occasional cases of AML show megakaryocytic or erythroid differentiation. Gene mutations are likely to become increasingly important in classification.
Table 20.1
WHO classification of acute myeloid leukaemia
AML with recurrent genetic abnormalities1
AML with inv (16)(p13;q22) or t(16;16) (p13.1;q22) (M4 Eo)
AML with t(15;17)(q22;q12) (M3:M3V)
AML with myelodysplasia-related changes
Therapy related myeloid neoplasms
AML not otherwise specified2
AML with minimal differentiation (M0)
Acute myelomonocytic leukaemia (M4)
Acute monoblastic/ monocytic leukaemia(M4/5)
Acute erythroid leukaemia (M6)
Myeloid sarcoma
Myeloid proliferation related to Down syndrome
Blastic plasmacytoid dendritic cell neoplasm