151 Morphologic Diagnosis of Acute Promyelocytic Leukemia (APL): How Well do We Do?

Abstract

Acute promyelocytic leukemia (APL) has a high incidence of disseminated intravascular coagulation. Thus, early recognition is critical. Cases exhibiting classical APL morphology are generally readily recognized; however, those exhibiting morphologic variability can be challenging and potentially initially missed. We were interested in determining our accuracy in diagnosing APL, based on morphology, in our clinical practice. Newly diagnosed cases of APL and randomly selected non-APL acute myeloid leukemia (AML) at our institution were identified. Pathologists reviewed peripheral blood/bone marrow aspirates blinded to the diagnosis, clinical, laboratory and genetic information. Cases were morphologically categorized into four groups: diagnostic of APL; suspicious, favor APL; suspicious, favor non-APL; and non-APL. These morphologic categorizations were compared with final diagnoses including genetic information. We reviewed 37 AML cases: 21 APLs and 16 non-APLs. Of the 21 APLs, 19 (90.5%) were “diagnostic of APL,” with one each of “suspicious, favor non-APL” and “non-APL.” Of 16 non-APLs, 15 were “non-APL,” and one “suspicious, favor non-APL.” The APL case miscategorized as “non-APL” had been recently diagnosed and treated with ATRA/cytarabine for APL with PML-RARA at an outside institution, imparting features of maturation in the initial bone marrow seen at our institution. The APL case categorized as “suspicious, favor non-APL” showed blasts with uniform bilobed nuclei and lacked multiple Auer rods or distinctive hypergranular forms. In this study, we were able to recognize about 90% of APL cases based on morphology. Importantly, knowing the patient’s clinical history and being aware of APL morphologic variations would improve our ability to provide an upfront diagnosis of APL. In suspicious cases, rapid FISH/molecular testing for PML-RARA fusion is critical to expedite detection of this recurring genetic abnormality.