DP030 | PROGNOSTIC IMPACT OF THE APL-LIKE CD34-HLA-DR IMMUNOPHENOTYPE IN NON-M3 ACUTE MYELOID LEUKEMIA: A RETROSPECTIVE STUDY

Background. Acute myeloid leukemia (AML) is a biologically and clinically heterogeneous disease. Among its subgroups, a distinct subset exhibits an APL-like immunophenotype, characterized by the absence of CD34 and HLA-DR expression. While this phenotype is a hallmark of acute promyelocytic leukemia (APL), its prognostic significance in non-APL AML remains unclear. Better characterization of this subset could improve risk stratification and treatment decisions. Methods. This retrospective study analyzed 425 adult non-M3 AML patients, identifying 31 (7.3%) with a CD34^-/HLA-DR^- immunophenotype. Clinical parameters, including complete blood count, bone marrow blast percentage, overall survival (OS), event-free survival (EFS), and relapse-free survival (RFS), were collected and compared with a control group. Both groups were comparable in risk stratification per the 2022 ELN classification. The impact of the APL-like phenotype on EFS, RFS, and relapse was assessed using Cox and logistic regression models. Results. Patients with the APL-like phenotype had a higher median bone marrow blast percentage (76.5% vs 64.0%, p = 0.018) and a trend toward more FLT3-ITD mutations (25.0% vs 13.1%, p = 0.077). They showed longer RFS (19.4 vs 10.6 months, p = 0.044) and EFS (8.71 vs 7.62 months, p = 0.044), with superior 1-year RFS (66.7% vs 42.9%) and EFS (42.9% vs 29.0%). OS was similar (18.6 vs 17.6 months, p = 0.910). Multivariable analysis confirmed the APL-like phenotype as an independent predictor of better EFS (HR 1.76, p = 0.023), while its effect on RFS was borderline (p = 0.061). Logistic regression did not identify it as an independent predictor of relapse (p = 0.935). Extramedullary involvement occurred in 22.6% of APL-like cases vs. 27.4% in controls (p = 0.217). Although it was linked to worse RFS (p = 0.004) and EFS (p = 0.046) in the overall cohort, its prevalence did not differ significantly between groups. Conclusions. The CD34^-/HLA-DR^- (APL-like) immunophenotype could define a distinct subset of non-M3 AML patients, associated with higher blast counts and a trend toward increased FLT3-ITD mutations. Despite these features, these patients exhibit significantly longer EFS and RFS, suggesting a more favorable course. While OS remains comparable to other AML subtypes, these findings highlight the potential prognostic relevance of this phenotype. Further studies in larger cohorts are needed to confirm these observations and explore therapeutic implications.