CXCR4 and acute lymphoblastic leukemia: In hematological malignancies, CD9 has been mainly studied in acute lymphoblastic leukemia (ALL) where it might promote cancer stem cell‐like properties and dissemination of the disease with CXCR4‐mediated migration.17, 18 Its role in AML remains controversial:a few studies suggested a pejorative role of CD9 with a decreased OS19 and a negative association with t(8;21)(q22;q22)20 while another study showed a correlation between CD9 and mutated NPM1 AML21 which are associated with a favorable prognosis.