A 27-year-old man presented with a 2-month history of fatigue and ecchymotic patches covering his body. On systemic examination, there was no organomegaly or lymphadenopathy. His hemoglobin was 8.6 g/dL, total leucocyte count was 2.1×10⁹/L, and platelet count was 32×10⁹/L. The patient was determined to be t (15;17) positive by PCR and FISH analysis, and was diagnosed with acute promyelocytic leukemia (APL) with Auer body formation surrounding the nucleus (A, B) based on a bone marrow aspirated smear image.

Auer rods are elongated, azurophilic cytoplasmic inclusions in myeloid leukemic blasts. Their presence confirms a diagnosis of acute myeloid leukemia. In APL, multiple such inclusion bodies may be observed, and may occur in clusters (faggots). Faggot cells are bundles of stick-like Auer rods formed by coalescence of primary granules. Their presence, although reported in other types of leukemia, is a morphological clue suggesting APL. They usually form random clusters in the cytoplasm of promyelocytes or blasts. To our knowledge, ring-shaped Auer body formation in a promyelocyte or blast resembling a Cabot ring in the erythrocyte has not been previously reported.