Clinical, histopathological and molecular characterization of extramedullary acute myeloid leukemia

Myeloid neoplasms, typically liquid tumors, may manifest as extramedullary (EM) masses, representing a significant diagnostic and therapeutic challenge. EM manifestations of acute myeloid leukemia (eAML), also called myeloid sarcoma (MS), constitute an unusual presentation or complication of AML, which can occur in isolation (isolated eAML) or in the context of a leukemic process (synchronous eAML). Genetic events and molecular mechanisms leading to eAML and the impact on clinical outcomes are not well understood and previous studies were limited mainly to small samples or case series, often with controversial results. The current study aims to clarify aspects of MS by i) examining a large monocentric cohort of newly diagnosed AML patients at the University of Florence (Careggi Hospital), comparing those with and without concurrent EM involvement; ii) analyzing the clinical, histopathological, and molecular profiles of 40 MS samples from 8 Italian Centers. 600 patients with newly diagnosed AML, after excluding 82 cases of acute promyelocytic leukemia (APL), were identified. 103/600 (17%) had eAML. Overall, 81% and 19% (n=119) had de novo and sAML, respectively. 494 (82%) patients were treated with intensive chemotherapy, and in 243 (41%) cases allo-HSCT was performed. Out of 539 evaluable patients, 245 (46%) had an abnormal karyotype of whom 71 cases (13%) had a complex karyotype. 140 (23%) were NPM1, 126 (21%) FLT3-ITD, 27 (5%) inv (16), 26 (4%) CEBPA bZIP, 24 (4%) t(8;21) mutated. Regarding baseline characteristics, patients with eAML were significantly younger (56 vs. 58 years, p=0.01), had higher white blood cell count (p< 0.01) and higher peripheral blood blast count (p= 0.02). Of interest, ELN 2022 favorable risk category (18% vs 31%, p=0.01) was significantly less common in eAML; conversely, intermediate category was more represented in eAML (42% versus 32%, p=0.03). FLT3-ITD (31% versus 19%, p<0.01) and TP53 mutations (22% versus 10%, 3 p=0.04) were significantly more common in eAML at diagnosis. Median overall survival including all 600 patients was 20.2 months (95% CI 15-25), significantly different for patients with (11 months) and without (23.5 months, p<0.01) eAML. The presence of >1 EM localization was associated with a less favorable outcome (HR 2; p<0.01) compared to cases with 1 EM localization. In multivariate analysis for OS, the presence of eAML (HR 1.4; p=0.02) along with older age (p<0.01), and ELN 2022 risk categorization (p<0.01) were significant for a reduced survival. Considering eAML only, ELN 2022 risk categorization lost the power to discriminate between intermediate and adverse category (p=0.4). Intensive chemotherapy and allo-HSCT were associated with superior OS in patients with and without eAML. Considering eAML only, SRSF2 (HR 3; p=0.03), SETBP1 (HR 10; p=0.04), and JAK2 (HR 4.9; p=0.04) mutations were associated with a reduced OS. When analyzing ELN 2022 genetic risk categories separately for patients with and without eAML, a significant different survival for intermediate risk patients was documented (HR 1.6; p=0.02); not in favorable (p=0.6), nor in adverse risk category (p=0.8). The whole exome sequencing (WES) of 25/40 MS, documented that 5,444 genes were mutated, with a median of 204 mutated genes per sample. The most frequent mutated genes were MDCAM1 (60%), PYGM (52%), DAGLA (48%), COL6A5 (40%), ZNF91 (40%). Our study represents one of the largest cohorts of eAML and establishes key molecular markers linked to EM, such as FLT3-ITD and TP53 mutations, providing evidence that eAML is associated with adverse risk features. Of interest, when considering eAML only, ELN 2022 risk categorization lost the power to discriminate between intermediate and adverse category, but a significantly different survival was maintained between favorable and intermediate category. Finally, intensive chemotherapy and allo-HSCT improved survival. A gene expression profile (GEP) analysis using NanoString technology is ongoing to complement the WES results, along with clinical, and histopathological features.