Methods for the diagnosis of leukemias, and more specifically AML, such as MLL-AF9 AML, in a subject, based on the assessment of the expression or activity of one or more of the genes listed in Tables 1 and 2 are disclosed. The use of antibodies or antigen-binding fragments thereof that bind to one or more of proteins showing preferential expression at the cell surface of AML leukemic cells for treating AML is also disclosed.