MCL1 and hypereosinophilic syndrome: In accordance with these results from the peripheral blood, the new MCL1 inhibitor S63845 showed high short- and long-term efficacy on the malignant stem and progenitor cell compartment of patients with a hypereosinophilic disorder, especially in BMMCs from patients with monoclonal hypereosinophilia (CEL-NOS and MLN-Eo).