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[Microgranular-type acute promyelocytic leukemia with weak myeloperoxidase staining: difficulty of morphological
Hiroka Matsuda1, Kyohei Misawa2, Tomonori Ochiai2
1Juntendo University Shizuoka Hospital.
Abstract:
The 2017 World Health Organization (WHO) classification states that acute promyelocytic leukemia (APL) always presents with strong myeloperoxidase staining. However, we herein report of a 40-year-old woman with the microgranular variant of acute promyelocytic leukemia presenting with weak myeloperoxidase (MPO) staining. The leukemic cells were morphologically similar to monocytic cells, showing distorted-shaped nuclei and weak MPO staining. However, flow cytometry revealed positivity of CD2, CD34, and human leucocyte antigen-DR (HLA-DR) and pointed toward a diagnosis of APL. PML-RARA mRNA detection finally led the patient to a definitive diagnosis. The patient achieved complete remission by induction chemotherapy including tretinoin, cytarabine and idarubicin, and no differentiation syndrome was observed.
Insights
This case study highlights a rare instance of microgranular acute promyelocytic leukemia (APL) with weak myeloperoxidase (MPO) staining, challenging the 2017 WHO classification. Definitive diagnosis relied on flow cytometry and PML-RARA mRNA detection, leading to successful treatment.
Area of Science:
- Hematology
- Oncology
- Molecular Diagnostics
Background:
- The 2017 World Health Organization (WHO) classification mandates strong myeloperoxidase (MPO) staining for acute promyelocytic leukemia (APL) diagnosis.
- The microgranular variant of APL typically exhibits specific morphological and immunophenotypic characteristics.
Observation:
- A 40-year-old woman presented with features of the microgranular variant of APL.
- Leukemic cells showed monocytic morphology, distorted nuclei, and notably weak MPO staining, deviating from the expected strong staining.
- Flow cytometry revealed positivity for CD2, CD34, and human leucocyte antigen-DR (HLA-DR).
Findings:
- The combination of weak MPO staining, specific morphology, and immunophenotypic markers initially posed a diagnostic challenge.
- PML-RARA mRNA detection was crucial for the definitive diagnosis of acute promyelocytic leukemia.
- The patient achieved complete remission with induction chemotherapy including tretinoin, cytarabine, and idarubicin, without developing differentiation syndrome.
Implications:
- This case expands the understanding of diagnostic variability in acute promyelocytic leukemia, particularly the microgranular variant.
- It underscores the importance of integrating multiple diagnostic modalities, including molecular testing, when classical markers are atypical.
- The findings suggest that APL can present with weak MPO staining, necessitating a broader diagnostic approach in clinical practice.
