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Emergence of a Ph-negative Clone in a Child With Ph+ ALL

The addition of tyrosine kinase inhibitors to conventional chemotherapy has improved outcomes for pediatric patients with Philadelphia chromosome-positive (Ph+) acute lymphoblastic leukemia (ALL). However, the rate of relapse is still higher compared with many other types of pediatric ALL, with many possible mechanisms for resistance. We describe an 8-year-old boy with Ph+ ALL relapsing with ALL without the Ph following treatment with dasatinib as a part of Children’s Oncology Group trial AALL1122. This emphasizes the polyclonal nature of ALL at diagnosis and indicates that the BCR-ABL fusion oncogene is not always an essential “driver” mutation.