EPO triggers STAT5 signaling in human ETV6-RUNX1⁺ ALL patient samples. CD19⁺ cells were isolated from ALL patients, grown in RPMI medium with or without EPO 20 U/mL for 1 hour, and lysates were analyzed by Western blot for STAT5 phosphorylation and BCL-XL expression. Only in ETV6-RUNX1⁺ patients with higher expression of EPOR was its ligand EPO able to trigger STAT5 signaling. BCL-XL expression was always higher in ETV6-RUNX1⁺ samples, although there was no difference in the presence or absence of EPO.