Although "paired box 5" (PAX5)-related fusion genes are well documented in childhood B-cell precursor acute lymphoblastic leukemia (ALL), these types of fusion with the exception of PAX5-JAK2 are rarely seen in patients with gene expression profiles similar to those of BCR-ABL1 (Philadelphia)-positive ALL (Ph-like ALL).
Having both a tyrosine kinase-activating rearrangement and genomic lesions affecting lymphoid transcription factors suggested that the leukemia was of the Philadelphia chromosome (Ph)/BCR-ABL1-like ALL subtype and that JAK2 inhibitors might be able to overcome this aggressive ALL with SPAG9-JAK2.
CRLF2 rearrangements, JAK1/2 point mutations, and JAK2 fusion genes have been identified in Philadelphia chromosome (Ph)-like acute lymphoblastic leukemia (ALL), a recently described subtype of pediatric high-risk B-precursor ALL (B-ALL) which exhibits a gene expression profile similar to Ph-positive ALL and has a poor prognosis.