Erythroid Leukemia Is Increased at High Altitude (4000 m)
Authors: Amaru Ricardo , Luna Leyza Maria Julieta , Mamani Luis Felipe , Mancilla Silvia , Paton Daniela , Valencia Juan Carlos , Carrasco Mireya , Amaru Ariel 
Published: December 2024

Acute erythroid leukemia (AEL) also known as pure erythroid leukemia (PEL) from the 2016 WHO update (PMID: 35264503; Wang, Am J Hematol. 2017; 92: 292-296) is a rare and unique subtype of acute myeloid leukemia (AML). It is characterized by immature erythroid precursors predominance with a high frequency of gains and amplifications involving EPOR/JAK2 (PMID: 35839275) and phosphorylation of ERK1/2 by inhibiting Fli-1 Promoter Activity (Min Mo, Catalysts, 2022. 13.1:84).

AEL accounts for 1% of AML cases and can evolve from prior myelodysplastic syndrome or develop de novo, it is typically observed in adults with a median age ranging 66-68 years, and of dismal prognosis (&lt;6 months overall median survival) (PMID: 36323674). Its distinction attributes to erythroblastic proliferation (&gt;80%), pancytopenia, and extensive bone marrow involvement by proerythroblasts (≥30%). Common immunophenotype markers include CD105, CD34, CD71, CD36, CD235 (Wang, Am J Hematol. 2017).

Moreover, it has been reported that hypoxia influences the development of erythroleukemia through various mechanisms, including promoting erythroid differentiation, inducing hemoglobin production, defining cell heterogeneity, regulating erythropoiesis, and influencing the bone marrow microenvironment (PMID: 33675821; 17255519). Regardingly, an overexpression of HIFs is related with a bad prognosis in AML (PMID: 25687039), HIF-1α is involved in cancer early stages, whereas HIF-2α in the later stages (PMID: 29753878). HIF-2a expression plays an important role in regulating proliferation in erythroleukemia cells under hypoxia (PMID: 26898802).

Thus, we aimed to search for the hematologic and immunophenotypic characteristics of AEL cases among all AML diagnoses at high altitude. We retrospectively analyzed cases of AML diagnosed in Bolivia from the period of May 2019 to April 2024 considering the different altitudes 4000m (n=68), 2000m (n=62), and 400m (n=71), and gathered a comprehensive account of hematologic, bone marrow morphology, and immunophenotypic features.

Among AML cases (n=201), 13 cases of AEL were identified which corresponded to 6.5 %. Interestingly, AEL cases at 4000 m accounted for 13.2 % (female 2, male 7, median age 54 years), and this was significantly higher (p=0.02) when compared to cases at 2000 m representing 3.2 % (female 1, male 1, median age 75 years) or at 400 m with 2.8 % (female 2, median age 52 years).

Hematologic indices displayed mean Hb 7.3 g/dl, WBC: 11515/ul and Plt: 127154/ul. Bone marrow findings reflected &gt; 80% of prominent erythroid precursors with large irregular nuclei, dispersed chromatin, 1 to 3 elongated nucleoli, deeply basophilic cytoplasm, and an intense mitotic activity. Immunophenotypic features revealed CD34, CD71, CD105, CD36 and CD235 regarding erythroid clonality.

AEL incidence is increased at high altitude, reflects intriguingly morphology and hematological characteristics. This increase may be due to the increase in HIF and Epo at high altitude, since the barometric pressure (462 mmHg) and the oxygen level in the air (14%) at high altitude are low. So, further studies elucidating the genetic mechanism involved are of interest.