Table of Contents
Definition / general | Diagnosis | Enzyme cytochemistry | Positive stains | Molecular / cytogenetics descriptionCite this page: Mihova D. AML M5. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/leukemiaacutemonocyticleukemia.html. Accessed April 25th, 2024.
Definition / general
- Acute monoblastic and acute monocytic leukemia (AML M5)
- 10% of AML cases
- High incidence of bleeding disorders (including DIC), organomegaly, lymphadenopathy, gingival hyperplasia, CNS and other tissue involvement (monocytes infiltrate)
- May present with acute respiratory failure (Am J Respir Crit Care Med 2003;167:1329)
- M5a versus M5b: analysis of features is controversial; (a) similar features (Leuk Res 2008;32:269); (b) different expression of CD68 and CD11c (Zhongguo Shi Yan Xue Ye Xue Za Zhi 2006;14:1079); (c) different features (Zhongguo Shi Yan Xue Ye Xue Za Zhi 2006;14:654)
- Similar prognosis as other subtypes (J Clin Oncol 2004;22:1276)
Diagnosis
- 80% or more nonerythroid bone marrow cells are monocyte lineage (monoblasts, promonocytes and monocytes)
- A minor neutrophil component < 20%
Enzyme cytochemistry
- Monoblast granules and monocytes are strongly positive for nonspecific esterase and lysozyme, but negative for myeloperoxidase
- More mature monocyte lineage cells may be weakly myeloperoxidase positive
- Note: if NSE negative, confirm monocyte lineage with immunostains
Positive stains
- At least two monocytic markers: CD4, CD14, CD11b (80 - 90%, Am J Clin Pathol 1997;107:283), CD11c (50%), CD36, CD64 (Am J Clin Pathol 1998;110:797), CD68 and HLA-DR
- Myeloid markers: CD13 (often very bright), CD33 (often very bright), CD15 and CD65
- CD34 (30%), CD117 and MPO (more often M5b and less often M5a)
- Abberant expression: CD7, CD56 (25 - 40%)
- Lysozyme, CD68 and CD163
Molecular / cytogenetics description
- 11q23 translocations in 19%, trisomy 8 in 17%
