Among other B-cell markers, B-I and B-II ALL are often CD24 positive and 4G7 (pro- and pre-B surrogate light chain specific MoAb) positive;16 surface CD20 and CD22 are variably positive beyond stage B-I; CD13 and CD33 myeloid/cross lineage antigen can be expressed, as well as the CD34 stem cell antigen, particularly in Ph+ (Philadelphia chromosome-positive) ALL (often B-II with CD34, CD38, CD25 and CD13/33), but myeloid-specific CD117 should not be present and can be used to differentiate further between ALL and rare myeloid leukaemias with negative MPO expression. The gene discussed is MPO; the disease is acute lymphoblastic leukemia.