The mutational and transcriptional landscape of P2RY8-CRLF2-positive ALL was defined in 41 major clone fusion-positive cases including 19 matched diagnosis and relapse pairs by an integrated analysis of whole-exome and RNA sequencing. We detected a variety of frequently subclonal and highly unstable JAK/STAT but also RTK/Ras pathway activating mutations in 76% of cases at diagnosis and virtually all relapses. Unlike P2RAY8-CRLF2 that was lost in 32% of relapses, all other genomic deletions affecting lymphoid development and cell cycle remained stable. Only IKZF1 alterations predominated in relapsing cases and increased from initially 36 to 58% in matched cases. IKZF1¹s transcriptional signature revealed compromised stem cell features with signs of impaired lymphoid differentiation, enhanced focal adhesion, activated hypoxia pathway, deregulated cell cycle and increased drug resistance.

The mutational and transcriptional landscape of P2RY8-CRLF2-positive ALL was defined in 41 major clone fusion-positive cases including 19 matched diagnosis and relapse pairs by an integrated analysis of whole-exome and RNA sequencing. We detected a variety of frequently subclonal and highly unstable JAK/STAT but also RTK/Ras pathway activating mutations in 76% of cases at diagnosis and virtually all relapses. Unlike P2RAY8-CRLF2 that was lost in 32% of relapses, all other genomic deletions affecting lymphoid development and cell cycle remained stable. Only IKZF1 alterations predominated in relapsing cases and increased from initially 36 to 58% in matched cases. IKZF1¹s transcriptional signature revealed compromised stem cell features with signs of impaired lymphoid differentiation, enhanced focal adhesion, activated hypoxia pathway, deregulated cell cycle and increased drug resistance.

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