PMC8337103_01
Bone marrow biopsy showing a hypercellular marrow with marked myeloid hyperplasia with left shift ((a) hematoxylin and eosin stain, 400x) and grade 3 fibrosis ((b) reticulin stain, 200x).
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fig1
Bone marrow (BM) biopsy demonstrated a hypercellular BM with left-shifted myeloid hyperplasia but less than 1% blasts (Figure 1(a)), an increased myeloid to erythroid ratio (>5 : 1) and diffuse grade 3 reticulin fibrosis (Figure 1(b)).
Fluorescent in situ hybridization with probes for BCR (22q11.2, green signal) and ABL1 (9q34.1, red signal) was negative for a BCR-ABL1 rearrangement. However, a third signal for the BCR probe (green signal, arrow) was observed, suggesting partial or complete gain of chromosome 22 or a translocation that involves BCR with a partner gene other than ABL1. Additional testing with a probe for JAK2 (9p24.1, not shown) suggested the presence of a BCR-JAK2 fusion, which was confirmed with RNA sequencing.
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fig2
Cytogenetics revealed a 46XY, del(6) (p21.2p24), t(22; 9; 11) (q11.2, p24, p11.2) /46XY, del(9) karyotype with fluorescent in situ hybridization (FISH) analysis showing absence of a BCR-ABL1 rearrangement, but three copies of BCR (Figure 2).
Lymph node showing extensive extramedullary involvement by a myeloproliferative neoplasm with numerous megakaryocytes ((a) hematoxylin and eosin stain, 400x), no increase in blasts ((b) CD34 immunostain, 400x), or significant myeloid cells ((c) MPO immunostain, 400x) but with prominent erythroid precursors ((d) CD71 immunostain, 400x).
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fig3
Excisional biopsy of a lymph node ruled out lymphoma, but revealed extensive extramedullary involvement of the same myeloid malignancy with prominent erythroid precursors, atypical megakaryocytes, and left-shifted myeloid cells without increase of blasts (Figure 3).