The curious case of HLA-DR-positive APL

Area of Science:

• Hematology
• Oncology
• Immunophenotyping

Background:

• Acute promyelocytic leukemia (APL) is a distinct subtype of acute myeloid leukemia.
• Accurate diagnosis is crucial for appropriate treatment and improved patient outcomes.

Observation:

• The typical immunophenotype for APL includes weak or absent CD34 expression.
• Negative or weak Human Leukocyte Antigen-DR (HLA-DR) expression is characteristic of APL.
• Strong positivity for CD117 (c-KIT) is a key diagnostic marker in APL.

Findings:

• The pathognomonic triad for APL diagnosis is weak/absent CD34, negative HLA-DR, and CD117 positivity.
• Atypical immunophenotypic profiles, including strong HLA-DR and CD34 positivity, can occur in rare APL cases.

Implications:

• Understanding these immunophenotypic variations is essential for accurate APL diagnosis.
• Flow cytometry findings require careful interpretation, especially in atypical presentations.
• Recognition of aberrant marker expression aids in differentiating APL from other myeloid neoplasms.