In contrast, mutations detected exclusively at relapse were frequently found in drug resistance-related genes in adult B-ALL (11/44, 25%): ABL1 mutations (T315I, Y253H and F359V) predominated in relapsed Philadelphia chromosome (Ph)-positive patients (6/7, 86%), while NT5C2 (R238L, R39Q and R667Q), NR3C1 (R714L and Q74fs), MSH6 (T1085fs) and CREBBP (S1436R) were mainly identified in relapsed Ph-negative patients (5/37, 14%). Here, MSH6 is linked to acute lymphoblastic leukemia.