The interest of molecular biology in both diagnosis, prognosis and treatment in AML with t(9;22)(q34.1;q11.2)/BCR::ABL1 is obvious since specific targeted therapies are already available and used both in chronic myeloid leukemia (CML) and AML, with a drastic improvement of prognosis, more particularly for patients unfit for allogeneic stem cell transplantation. The gene discussed is BCR; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.