Abstract
Faggot cells are abnormal cells containing multiple Auer rods in the cytoplasm. They are usually found in acute
promyelocytic leukemia (APL), typically characterized by PML::RARA fusion. We describe a rare case in which
faggot cells were observed, but the patient was ultimately diagnosed with acute myeloid leukemia (AML) with
NUP98::HOXA9. A man in his 40s presented with fever, pneumonia, and coagulopathy. Peripheral blood examination
revealed an increased number of blast cells with Auer rods. Bone marrow (BM) aspirate smears showed
the proliferation of abnormal promyelocyte-like cells showing strong myeloperoxidase positivity; some contained
multiple Auer rods, consistent with faggot cells. Flow cytometric analysis of the BM revealed an APL-like immunophenotype,
characterized by the expression of myeloid markers and the absence of CD34 and HLA-DR.
Based on these morphological and immunophenotypic findings, the patient was initially suspected to have APL
and was treated with all-trans retinoic acid (ATRA) in combination with cytotoxic induction chemotherapy. However,
subsequent molecular analyses revealed the presence of NUP98::HOXA9 mRNA and absence of PML::RARA
mRNA. Therefore, APL was excluded, and the patient was diagnosed with AML with NUP98 rearrangement.
Consequently, ATRA was discontinued. Chromosomal analysis revealed the presence of t(7;11)(p15;p15),
supporting the revised diagnosis. Despite exhibiting APL-like morphological and immunophenotypic features,
the disease was ultimately diagnosed as non-APL AML based on genetic and chromosomal testing. This case
highlights the fact that faggot cells are not entirely specific for APL and emphasizes the importance of integrating
morphological, immunophenotypic, and genetic/cytogenetic findings for accurate diagnosis and appropriate
treatment.
