SSBP2-CSF1R is a recurrent fusion in B-lineage acute lymphoblastic leukemia with diverse genetic presentation and variable outcome

TO THE EDITOR:

Philadelphia chromosome (Ph)-like/BCR-ABL1–like acute lymphoblastic leukemia (ALL; Ph-like ALL) defines a subgroup of B-cell precursor ALL (B-ALL) lacking the BCR-ABL1 fusion, with a similar gene-expression profile to BCR-ABL1⁺ ALL and high risk of relapse.^1-3  Ph-like ALL represents a genetically heterogeneous group, including a number of fusions, which involve the ABL-class genes: PDGFRB/A, CSF1R, ABL1, and ABL2.^4-6  Preclinical studies have shown that leukemic cells from patients with these fusions respond well to tyrosine kinase inhibitors (TKIs),⁴  which has been confirmed in a number of patients, particularly those with EBF1-PDGFRB fusions.^7-10  Here, we focus on the genetic and clinical features of a rare subset of ABL-class patients with the SSBP2-CSF1R fusion. In particular, we reveal the diversity of cytogenetic changes, giving rise to the fusion, highlighting that awareness of...