An Acute Promyelocytic Leukemia Resistant to All-Trans Retinoic Acid: A Case Report of the ZBTB16::RARa Variant and Review of the Literature.

Acute promyelocytic leukemia (APL) is characterized by the PML::RARa gene fusion and treatment consists of all-trans retinoic acid (ATRA). Rarely, genetic APL variants have been described which are insensitive to ATRA treatment and are therefore associated with a worse prognosis. Rapid identification of the APL variant is essential to start the correct treatment. Here, we present a case of a 66-year-old male patient with weight loss and arthralgia. Laboratory results showed an anemia and mild leukocytosis with predominantly monocytes. Bone marrow investigation unexpectedly revealed a t(11;17)(q23;q21). This raised suspicion of an ATRA-resistant APL. By demonstrating the ZBTB16::RARa gene fusion, the diagnosis was confirmed. This case study emphasizes the importance of integrated diagnostics and provides guidance to recognize the ZBTB16::RARa APL, which is the most prevalent ATRA-resistant APL. Furthermore, an overview of other genetic APL variants is presented and how to treat these uncommon diseases in clinical practice.