Acute lymphoblastic leukemia (ALL) is a cancer of the blood that originates in the hematopoietic cells in bone marrow. It is the most common type of cancer in children (NCI 2012). Together, leukemias represent 26% of cancer diagnoses in children under the age of 20; ALL makes up 78% of leukemia cases in children under the age of 15 (SEER 1999). Approximately 2,400 children are diagnosed with ALL in the U.S. each year (SEER 1999). The five-year survival rate for children with ALL is over 80% (SEER 1999). In all age groups, 6,590 ALL diagnoses and 1,430 deaths are expected in the U.S. in 2016 (ACS 2016).

In ALL, normal differentiation of blood stem cells in the bone marrow is disrupted along B- or T-cell lineage development (NCI 2012). ALL is divided into subtypes based on tumor cell immunophenotype and histology: lymphoblasts of B-, T-, or biphenotypic lineage. (NCI 2012). Childhood ALL is generally treated with 2-3 years of chemotherapy, beginning with remission induction therapy, followed by postinduction consolidation/intensification therapy and maintenance therapy (NCI 2012).

Each of the main subtypes of ALL has characteristic molecular features; many of these have prognostic significance (Harrison 2011). For precursor B-cell ALL, the uses of tyrosine kinase inhibitors, CD19 antibodies, and CD20 antibodies as targeted therapeutics have all been explored (Oyekunle et al. 2011). Recently, preclinical models have been used to test efficacy of mTOR and JAK inhibitors in CRLF2-rearranged and JAK2-mutated high-risk precursor B-cell ALL (Maude et al. 2011). JAK2 inhibitors are currently being tested in phase I clinical trials.