Dual lympho-myeloproliferative disorder in a patient with t(8;22) with BCR-FGFR1 gene fusion.

The case of a patient presenting with a myeloproliferative disorder (MPD) characterized by a t(8;22) (p12;q11) translocation was investigated. The rearrangement resulted in the production of BCR-FGFR1 and FGFR1-BCR chimeric transcripts after in-frame fusions of BCR exon 4 with FGFR1 exon 9 and FGFR1 exon 8 with BCR exon 5, respectively. The four previously reported patients with such translocation presented with an atypical chronic myeloid leukemia (CML) without Philadelphia chromosome. In addition to a myeloproliferation, the patient had a B cell proliferation. The phenotypic characterization of the lymphoid cells in the bone marrow showed a continuum of maturation from blast B cells to polyclonal lymphocytes. In the blood, B cells showed a complete polyclonal maturation. The BCR-FGFR1 gene fusion was detected by dual-color fluorescence in situ hybridization in both CD19- and CD19+ populations. In contrast to the other FGFR1-MPDs that show myeloid and T cell proliferation, we propose that this t(8;22) MPD is a myeloid and B cell disease, and potentially a novel type of hematological disease. Although the FGFR1-MPD is rare, its study provides interesting clues to the understanding of hematopoietic stem cell biology and oncogene activation.