FAB Classification of AML-4
M5:
Acute
Monocytic Leukemia 12%
of AML cases
>30%
of marrow nucleated cells are blasts
M:E
ratio >1 - NSE positive in >80%
of blasts
>80%
of bone marrow cells have monocytic features
Two
subtypes found:
<20%
of bone marrow cells are granulocytic
>80% of monocytic cells
are monoblasts
Monoblasts have delicate
chromatin, prominent nucleoli, dark blue to gray budding cytoplasm
Patients are younger, have
elevated blasts, and poorer prognosis
Poorly
differentiated (M5a)
Differentiated
(M5b)
<80% of monocytic cells
are monoblasts
High % of pb cells are
mature monocytes