Acute promyelocytic leukemia: Immunophenotype and differential diagnosis by flow cytometry
Hong Fang1, Sa A Wang1, Shimin Hu1
1Department of Hematopathology, The University of Texas MD Anderson Cancer Center, Houston, Texas, USA.
Insights
Prompt diagnosis of acute promyelocytic leukemia (APL) is crucial. Flow cytometry immunophenotyping can distinguish APL from mimics like NPM1-mutated AML and KMT2A-rearranged AML using markers such as CD2, CD13, CD34, CD64, and MPO.
Area of Science:
- Hematology
- Immunophenotyping
- Flow Cytometry
Background:
- Accurate diagnosis of acute promyelocytic leukemia (APL) is vital for effective patient management.
- Immunophenotypic characterization aids in differentiating APL from similar hematologic malignancies.
Purpose of the Study:
- To characterize the immunophenotype of APL using flow cytometry.
- To identify immunophenotypic differences between APL and its mimics, including NPM1-mutated AML and KMT2A-rearranged AML.
Main Methods:
- Flow cytometric analysis was performed on 85 cases: 47 APL, 26 NPM1-mutated AML, and 12 KMT2A-rearranged AML with APL-like immunophenotypes.
- Immunophenotypes were analyzed based on CD45/SSC plots and specific marker expression.
Main Results:
- APL exhibited four distinct patterns (a-d) on CD45/SSC plots, with pattern d (APL-D) showing distinct characteristics.
- APL-D cases were more frequently positive for CD2 and CD34 compared to NPM1-mutated AML.
- CD13 and CD64 expression were highly characteristic of APL-D, while KMT2A-rearranged AML showed distinct patterns in MPO and CD2/CD34 expression.
Conclusions:
- APL and its immunophenotypic mimics share similarities but can be reliably distinguished.
- Specific markers including CD2, CD13, CD34, CD64, and MPO are key for differentiating APL from NPM1-mutated AML and KMT2A-rearranged AML.
Background:
Prompt diagnosis of acute promyelocytic leukemia (APL) is critical for patient care. In this study, we aimed to characterize the immunophenotype of APL and explore immunophenotypic difference between APL and its mimics using flow cytometric analysis.
Methods:
Eighty-five cases were collected, including 47 APL, 26 NPM1-mutated acute myeloid leukemia (AML) and 12 KMT2A-rearranged AML with an APL-like immunophenotype. Immunophenotypes were analyzed using flow cytometric analysis.
Results:
APL showed four distinct patterns (designated a-d) based on CD45/SSC plots. Blasts in patterns a-c showed high side scatter, whereas blasts in pattern d had low side scatter and were located in the traditional blast gate. Compared with patterns a-c, pattern d of APL (APL-D) was more often positive for CD2 (p = 0.0005) and CD34 (p = 0.0002) in blasts. All NPM1-mutated AML and KMT2A-rearranged AML cases with an APL-like immunophenotype had blasts in the traditional blast gate on CD45/SSC, mimicking APL-D. In comparison, uniform CD13 and positive CD64 were seen in 100% (n = 13) APL-D cases and in only 2 of 26 (8%) NPM1-mutated AML cases (p < 0.0001). In addition, APL-D cases were more likely to be positive for CD2 and/or CD34 than NPM1-mutated AML (p < 0.0001 and p = 0.0007, respectively). In comparison with APL-D, KMT2A-rearranged AML cases were less often positive for myeloperoxidase (MPO) (p = 0.001), with none being strongly positive. Similar to NPM1-mutated AML and different from APL-D, KMT2A-rearranged AML cases were rarely positive for CD34 and all negative for CD2.
Conclusions:
APL and its immunophenotypic mimics share some immunophenotypic similarities but can be distinguished by CD2, CD13, CD34, CD64, and MPO.
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