Distinctive features associated with differentiation syndrome in acute promyelocytic leukemia in patients treated by all-trans retinoic acid and arsenic trioxide.

In acute promyelocytic leukemia (APL), the combination treatment of all-trans retinoic acid (ATRA) and arsenic trioxide (ATO) appears to have a synergistic effect. Due to this synergism, differentiation syndrome (DS) in APL assumes a distinct identity separate from the formerly known ATRA syndrome, with distinct temporal patterns, diagnostic parameters, and clinical behavior. We retrospectively evaluated single-center data of years 2013-2022. Patients with newly diagnosed APL were categorized into three groups (16 patients in ATRA/ATO standard-risk group, 3 patients in ATRA/chemotherapy standard-risk group, and 5 patients in ATRA/chemotherapy high-risk group). Our aim was to analyze leukocytosis, signs of DS, and hepatic impairment within the first 25 days of treatment. The incidence of DS in the ATRA/ATO SR group was 43.8 %, with a median of 4 days and 2 days from ATRA and ATO initiation, respectively. This group also exhibited higher peak levels of leukocytosis 34.5 (6.0-113.4) x10/L (p = 0.0809). ALT elevation was more prevalent in the ATRA/ATO SR group (93.75 %), with 68.75 % grade 3-4 elevations (p = 0.0094). Importantly, all patients in this group had ALT levels that returned to normal during the subsequent consolidations. These findings suggest hepatopathy as a potential manifestation of ATRA/ATO induced leukocyte differentiation and/or DS. Diverse differentiation patterns were identified within the ATRA/ATO group, classifying patients into three distinct subgroups based on the concurrent dynamics of leukocytes and ALT levels, illustrating simultaneous, sequential, and divergent elevation patterns. These emphasize the different distribution of differentiation (organs vs. peripheral blood). We introduced real-world data and advocated for reevaluation of the current DS definition and associated diagnostic thresholds. Our study, conducted in a small country with a limited number of APL patients, acknowledges the inherent constraints in sample size. Further investigations with larger patient cohorts are warranted to validate and reinforce the outcomes observed in our study.