Marking over a century of Auer rods: An illustrated review of acute promyelocytic leukemia

In 1903, Dr. John Auer first observed needle-like rods in what he initially mistook for lymphocytes from a patient with fever, coagulopathy, and splenomegaly. Later discovered in myeloblasts, these “Auer rods” emerged as a defining feature of myeloid malignancies. Among them, acute promyelocytic leukemia (APL), recognized as a distinct clinical entity in 1957, was once considered the most lethal acute leukemia due to its severe coagulopathy and alarmingly high early mortality rate. However, landmark breakthroughs, particularly the introduction of all-trans retinoic acid in the 1980s and arsenic trioxide in the 1990s, transformed APL into the most curable form of acute leukemia, provided that treatment begins early. This illustrated review highlights over a century since Auer rods were first identified, offering a concise, visually guided overview of APL’s epidemiology, clinical presentation, and diagnostic strategies. We explore modern and practical therapeutic approaches, emphasize risk-adapted treatments, and address major complications, including differentiation syndrome, coagulopathy, and central nervous system involvement. The remarkable evolution of APL—from a highly fatal disease to the most treatable leukemia—highlights how our understanding of disease pathophysiology and biology can transform treatment strategies and improve patient outcomes.