The treatment of CML has changed from chemotherapeutic agents (hydroxyurea and busulfan) since 1959–1982, and interferon-alpha or allogeneic stem cell transplantation in 1983–2000, to BCR–ABL1 tyrosine kinase inhibitors (TKIs), introduced in 2001 [7]. The gene discussed is BCR; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.