The t(9;22)(q34;q11.2), also known as the Philadelphia (Ph) chromosome, results in BCR-ABL1 fusion residing on the derivative chromosome 22. This translocation is characteristic of chronic myeloid leukemia, but also can occur in a substantial subset of B acute lymphoblastic leukemia (B-ALL) cases. Ph-like B-ALL has a gene expression profile similar to that of BCR-ABL1 positive/Ph-positive B-ALL, but by definition Ph-like B-ALL does not have the sentinel BCR-ABL1 or the Ph chromosome. About half of Ph-like B-ALL cases carry CRLF2 rearrangements. Rare cases of de novo B-ALL with co-occurrence of BCR-ABL1 and CRLF2 rearrangements have been described. To our knowledge, this is the first report of concurrent BCR-ABL1 and CRLF2 rearrangements in blast phase of chronic myeloid leukemia. In this patient, CRLF2 rearrangement was acquired at the time of disease progression to B-lymphoblast phase of chronic myeloid leukemia. We also review the literature and discuss the distinct clinicopathologic, and genomic characteristics of CRLF2 rearranged B-ALL.
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