Role of flow cytometry in the diagnosis of acute promyelocytic leukemia

Immunophenotypic Profiling of Acute Promyelocytic Leukemia: Insights From a Large Cohort

BACKGROUND

Acute promyelocytic leukemia (APL) is a highly aggressive disease that requires early initial therapy. Rapid diagnosis by flow cytometry remains the mainstay of initial diagnosis. However, the complexity of its immunochemistry has led to diagnostic uncertainty.

METHODS AND RESULTS

We comprehensively reviewed 2124 AML patients, with 170 classified as APL. In the univariate analysis, HLA-DR, CD34, CD56, CD11b, and CD11c were predominantly positive in the non-APL group compared to the APL group, while MPO and CD33 were significantly positive in the APL group. In the multivariate analysis, MPO was identified as a significantly higher positive marker in APL patients, while HLA-DR, CD34, and CD56 predicted non-APL patients. The typical immunophenotype of APL, including MPO+/HLA-DR-/CD34- and CD117+, provided a sensitivity of 51.4%, a specificity of 98.0%, a positive predictive value of 65.8%, and a negative predictive value of 96.5%. By utilizing the decision tree methodology, HLA-DR, MPO, and CD34 emerged as pivotal indicators for APL diagnosis within this model. Notably, HLA-DR took precedence, followed by MPO and CD34. Ultimately, a predictive equation for APL diagnosis was proposed to simplify the diagnosis of APL by flow cytometry using the positivity of HLA-DR, MPO, and CD34 as reference points.

CONCLUSION

This study underscores the role of immunophenotyping as a rapid and complementary tool to molecular diagnostics, aiding in the preliminary identification of probable APL cases and facilitating timely initiation of therapy.

High-Risk Acute Promyelocytic Leukemia with Unusual T/Myeloid Immunophenotype Successfully Treated with ATRA and Arsenic Trioxide-Based Regimen

We describe two patients with acute promyelocytic leukemia (APL) with an unusual immunophenotype with co-expression of myeloperoxidase (MPO) with cytoplasmic CD3 (cCD3) representing myeloid and T-lineage differentiation. Both harbored FLT3-ITD mutations. One additionally had a deletion in the PML gene affecting the primer binding site, thus limiting measurable residual disease (MRD) analysis during follow-up. Both patients achieved durable remission with all-trans retinoic acid (ATRA) and arsenic trioxide (ATO)-based therapy, thus mitigating the need for repetitive conventional chemotherapy cycles and allogeneic stem cell transplantation. Our report highlights the complexity and challenge of diagnosis and management of APL due to the variant immunophenotype and genetics, and underscores the importance of synthesizing information from all testing modalities. The association of the unusual immunophenotype and FLT3-ITD mutation illustrates the plasticity of the hematopoietic stem cell and the pathobiology of leukemia with mixed lineage or lineage infidelity.

Diagnostic immunophenotype of acute promyelocytic leukemia before and early during therapy with all-trans retinoic acid

OBJECTIVES

To study the immunophenotypic changes of acute promyelocytic leukemia (APL) in patients who recently received all-trans retinoic acid (ATRA) and to assess the diagnostic utility of flow cytometry in this setting.

METHODS

Flow cytometry was performed on 29 newly diagnosed APLs and 93 other acute myeloid leukemias, including 25 HLA-DR- or CD34- cases. Clinical notes from referring institutions were reviewed to assess for recent ATRA administration.

RESULTS

Recent ATRA therapy was documented in 17 (59%) of 29 patients with APL. The main features of untreated APL were preserved with ATRA therapy, including CD34- (83% vs 82%), HLA-DR- (83% vs 100%), and CD117+ (100% vs 77%). CD11b and CD11c were negative in all untreated APLs but positive in 76% and 88% of ATRA-treated APLs, respectively. Optimal diagnostic criteria for untreated APL (CD34- or HLA-DR- and CD11b- and CD11c-) showed 100% sensitivity and 98% specificity but were not useful after ATRA administration. The best interpretative approach to ATRA-treated APL (CD34- or HLA-DR-) showed 100% sensitivity but limited specificity (73%).

CONCLUSIONS

Information about recent ATRA administration is critical for adequate interpretation of the flow cytometric findings in patients with suspected APL.