At the time of resistance to therapy with the tyrosine kinase inhibitor (TKI) imatinib, a proportion of Philadelphia chromosome-positive (Ph+) leukemia patients ranging from 30 to 70% – depending on disease phase and type – are found to carry mutations in the BCR-ABL1 kinase domain (KD) when analyzed by Sanger sequencing (SS) [1, 2]. The gene discussed is BCR; the disease is leukemia.