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.