The appearance of "faggot Auer rods" in blasts of non-M3 acute myeloid leukemia.

BACKGROUND: Acute myeloid leukemia (AML) is an acute leukemia characterized by aberrant proliferation of myeloid blasts in the bone marrow. Auer bodies are identifiable in the blasts of certain AML subtypes, but their "faggot-like" aggregation is uncommon, associated with strong peroxidase positivity, and readily misidentified as abnormal promyelocytes.

CASE PRESENTATION: A 79-year-old male was admitted for leukocytosis detected on physical examination. One month prior, he had marked leukocytosis (unspecified value) with predominant monocyte elevation. Admission complete blood count (CBC) confirmed leukocytosis and elevated monocyte percentage. Peripheral blood (PB) smear demonstrated 35% abnormal leukocytes, and bone marrow (BM) aspirate revealed these cells accounting for 40%. Morphologically, the cells had round nuclei and abundant cytoplasmic granules, with most of the cytoplasm filled with "faggot-like" Auer bodies (strongly positive for peroxidase). Flow cytometry revealed blasts positive for CD117, CD33, and MPO, with minimal positivity for CD13. Further investigations (leukemia fusion gene detection, FISH, chromosome Analysis, next-generation sequencing, and whole-transcriptome sequencing) failed to detect any APL-specific fusion genes, and the patient was ultimately diagnosed with non-M3 subtype AML.

CONCLUSION: This case is a special type of acute myeloid leukemia (AML) with morphological features highly resembling acute promyelocytic leukemia (APL) but without the associated fusion gene. Faggot-like Auer bodies, once considered a hallmark of APL, are not pathognomonic for APL, and diagnosis based solely on morphology is susceptible to misdiagnosis. This report aims to accumulate clinical experience, provide a reference for the diagnosis and management of similar cases, and reduce the incidence of misdiagnosis and missed diagnosis.