Acute Myeloid Leukemias and Precursor Lesions Flashcards
What are the necessary criteria
for the diagnosis Acute Monoblastic and
Monocytic Leukemia ?
- peripheral blood and bone marrow >20% blasts (including promonocytes)
- >80% of the leukemic cells must be monocytic
- monoblasts, promonocytes, monocytes
- minor neutrophil component can be present <20%
How are acute monoblastic leukemia and
acute monocytic leukemia distinguished ?
- >80% of leukemic cells are monoblasts in acute monoblastic leukemia
- Acute monocytic leukemia most leukemic cells are promonocytes and monocytes
IMP: neither entity can fulfill criteria for AML with recurrent cytogenetics or MDS related changes.
- considered FAB M5 classification
What are key epidemiological features of
Acute monoblastic or monocytic leukemia ?
Acute Monoblastic Leukemia:
- represent <5% of cases of AML
- most common in young individuals
- Extramedullary lesions are common
Acute Monocytic Leukemia:
- <5% of AML cases
- more common in adults, >40 years old
What are the clinical features
of acute monoblastic or monocytic leukemia ?
- present with bleeding disorders
- extramedullary masses
- cutaneous and gingival infiltration
- CNS involvement is quite common
What is the morphology of
monoblasts ?
- large cells with abundant cytoplasm which is moderate to intensely basophilic and pseudopod formation can be seen
- vacuoles and scattered azurophilic granules can be seen
- nuclei: round, delicate lacy chromatin, one or more prominent nucleoli
What is the morphology of
Promonocytes ?
- more irregular, delicately convuluted nuclei
- cytoplasm is less basophilic compared to the monoblasts
- can have more pronounced granules, prominent azurophilic granules, and occasional vacuoles
Note: Auer rods are rare, more common in myeloblasts
What is a frequent complication
of Acute Monoblast or monocytic leukemia?
- Hemophagocytosis (HLH)
- often associated with t(8;16)(p11.2;p13.3)
- can also be seen with Acute myelomonocytic leukemia or some cases of AML with maturation
What is the morphology in the bone marrow
in Acute Monoblastic or Acute monocytic
leukemia?
- usually hypercellular marrow
- predominant population of large, poorly differentiated blasts with abundant cytoplasm
- Nucleoli may be prominent
- Promonocytes show nuclear segmentation
Extramedullary disease: composed predominantly of monoblasts, promonocytes or an admixture
What is the characteristic cytochemistry
of monoblasts and promonocytes ?
- intense, NSE (non-specific esterase)
- 10-20% are negative or only weakly positive
- may need IHC to type them
- IHC
- Monoblasts - MPO negative
- Promonocytes - some scattered MPO positivity
What is the major differential diagnosis for
acute monocytic leukemia ?
- CMML
- Acute myelomonocytic leukemia
- Microgranular APL
- APL promyelocytes will be intensely MPO + and Napthol AS-D chloroacetate esterase (CAE)
What is the immunophenotype by Flow Cytometry of
Acute Monoblastic and/or Acute Monocytic Leukemia ?
- Variable expression of Myeloid Markers:
- CD13, CD33 (often very bright), CD15, CD65
- Expression of at least 2 monocytic markers:
- CD4, CD14, CD11b, CD11c, CD64(bright), CD68, CD36(bright), Lysozyme
IMP: CD34 is only + in 30% of cases
- CD117 (KIT) is more often expressed
- HLA-DR: positive in most cases
- CD7 and CD56 found in 25-40% of cases
What markers are useful by IHC
in tissue sections for diagnosis of Acute monoblastic or
acute monocytic leukemia ?
- Lysozyme (can be positive in AML without monocytic differentiation)
- CD68
- CD163
What are key genetic/molecular changes
encountered in Acute Monoblastic or Acute Monocytic Leukemia?
- t(8;16)(p11.2;p13.3)
- can be associated with HLH and coagulopathy
