CD33 and acute lymphoblastic leukemia: This served as the rationale for defining ETP-ALL under the latest WHO 2017 classification: positive intracytoplasmic CD3 expression and CD7 expression, CD1a-negative, CD8-negative, negative or dim expression of CD5 (<75% positive), and positive (≥25% of blasts population) for at least one stem cell or myeloid antigen, including CD34, HLA-DR, CD13, CD33, CD117, CD11b, and CD65 (4, 7).