FGFR1-associated myeloid neoplasm with increased mast cells.

Abstract

A 36-year-old man presented with left upper quadrant pain and was found to have significant splenomegaly, anaemia (Hb 98 g/l), thrombocytopenia (platelet count 90 × 109/l) and leucocytosis (WBC 59·7 × 109/l) with a differential of 41% neutrophils, 5·5% lymphocytes, 8·5% monocytes, 5% eosinophils, 3% basophils, 2·5% blasts, 2% promyelocytes, 19% myelocytes and 13·5% metamyelocytes. His bone marrow was 100% cellular with increased eosinophils and precursors (21%), 4% blast cells and the translocation t(8;13)(p11;q12), with fluorescence in situ hybridization (FISH) studies confirming rearrangement of FGFR1. Mast cells were mildly increased in the aspirate film and on immunostaining of a trephine biopsy section, and became more prominent on subsequent marrow evaluations. Splenectomy revealed myeloid sarcoma with effacement of the architecture by sheets of blast cells, as well multifocal mast cell aggregates. The CD34+ CD117- immunophenotype of the blasts (top left) distinguished them from the CD117+ mast cells (top right), which also showed aberrant expression of CD25 by flow cytometry. Both areas showed FGFR1 rearrangement by FISH studies (bottom). Abnormal mast cell proliferations overlapping morphologically with systemic mastocytosis have been described in myeloid and lymphoid neoplasms with eosinophilia and rearrangements of PDGFRA or PDGFRB. We present a case of FGFR1-associated myeloid neoplasm with a prominent mast cell proliferation mimicking systemic mastocytosis; increased mast cells should be recognized as a feature that is sometimes present in this condition. Unfortunately, the prognosis is poor, and the patient's disease relapsed despite fully ablative haploidentical peripheral blood stem cell transplantation.