The results of a diagnostic work-up of a patient with CRLF2-rearranged BCR/ABL1-like ALL. a FISH analysis with CRLF2 break-apart probe (CytoCell®) in HR B-ALL patient with high CRLF2 expression on leukemic blasts in FC. In the normal cell, 2 red/green signals (or yellow, Y) are observed (2Y). Cells with 1 green signal and 1 fused red/green signal (1G, 1Y) may carry an intrachromosomal deletion resulting in the presence of P2RY8-CRLF2 fusion gene (pointed with arrow). b Second step analysis with P2RY8 deletion probe (CytoCell®). In a normal cell, 2 red/green signals (2R, 2 G) are expected. Cells with 1 red and 2 green signals (1R, 2 G) carry a hemizygous deletion resulting in the presence of P2RY8-CRLF2 rearrangement (personal data). HR, high risk; CRLF2, cytokine receptor-like factor 2; FISH, fluorescent in-situ hybridization; FC, flow cytometry.