Acute leukemia with cytogenetically cryptic FGFR1 rearrangement and lineage switch during therapy: A case report and literature review.

OBJECTIVES: Myeloid/lymphoid neoplasms with FGFR1 rearrangement are a rare group of neoplasms that share features of eosinophilia and lineage promiscuity. First, we described a challenging case of acute leukemia with lineage switch and cytogenetically cryptic FGFR1. Second, we aimed to systemically review this phenomenon in published literature. METHODS: A 68-year-old man with a history of chemotherapy exposure presented with acute leukemia of myeloid lineage without eosinophilia or 8p11 abnormalities on karyotyping. Over a refractory and relapsing course, the blast phenotype shifted to B lymphoid. RESULTS: Fluorescence in situ hybridization identified a cytogenetically cryptic FGFR1 rearrangement, likely a paracentric inversion. We identified 26 published cases of FGFR1-rearranged acute leukemia with ambiguous, mixed, or switching lineage. Although there was variability in the partner gene, anatomical location of different phenotypes, and timing of lineage switch, the prognosis was consistently poor in the absence of novel therapy. CONCLUSIONS: Ours is the only reported case of FGFR1-rearranged neoplasms with a disease sequence of acute myeloid leukemia transforming to B-cell acute lymphoblastic leukemia and 1 of only 3 reported cases with cytogenetically cryptic FGFR1 rearrangement. Fluorescence in situ hybridization testing for FGFR1 rearrangement should be a standard investigation in leukemia of mixed or switching lineage.

Increased circulating normal and BCR-ABL+Ve progenitor numbers in Philadelphia chromosome-positive acute myeloid leukaemia.

We recorded elevated numbers of circulating myeloid and erythroid colony-forming cells in 15 adult patients with acute myeloid leukaemia (AML) who presented with high blood white cell counts. Since leukaemic blasts from three of these patients were Philadelphia chromosome-positive (Ph+), we were able to determine if blood progenitors from these particular patients arose from the leukaemic clone or from residual normal progenitors. Blasts and colonies were intensively investigated using a combination of cell surface marker analysis by flow cytometry, RT-PCR and interphase fluorescence in situ hybridization (FISH). FISH detected rearrangements within the major breakpoint BCR (M-BCR) region in blasts and in some myeloid and erythroid colonies from patients 1 and 2. The minor breakpoint (m-BCR) region was detected in blasts and in some myeloid and erythroid colonies from patient 3. RT-PCR detected long b2a2 BCR-ABL transcripts in blasts from patients 1 and 2, although misspliced short e1a2 transcripts were also seen in patient 1. Only e1a2 transcripts were found in blasts from patient 3. Flow sorting demonstrated the B-cell marker CD19 on blasts and on a proportion of myeloid and erythroid progenitors from patients 1 and 3. RT-PCR also detected IgH rearrangements, further evidence of B-cell differentiation, in blasts from these two patients. We conclude that both normal and clonal circulating progenitor numbers can be raised in both M-BCR and m-BCR Ph+ AML. The underlying cause, perhaps efflux from a congested marrow, may be common to AML patients with a high blood white cell count.