Hematogones in the bone marrow of adults. Immunophenotypic features, clinical settings, and differential diagnosis.

Hematogones (HGs) comprise a B-lineage lymphoid precursor cell population in the bone marrow (BM) that may simulate acute lymphoblastic leukemia or lymphoma. Increased numbers of HGs have been noted in children, but few reports describe their occurrence in adults. We identified 13 adult patients with significant numbers of BM lymphoid cells with the morphologic and immunophenotypic features of HGs. Common features in these patients included (1) presence of small numbers of lymphoid cells in the BM aspirate with morphologic features of HGs; (2) absence of cytologic atypia or abnormal localization of lymphoid cells in the BM biopsy; (3) absence of abnormal morphology or CD10 (common acute lymphoblastic leukemia antigen) expression in circulating lymphocytes; (4) normal BM karyotype; (5) persistence of cytopenia(s) without apparent cause, often for a prolonged period of time; and (6) no evidence of neoplastic marrow involvement, confirmed by clinical follow-up. Flow cytometry demonstrated surface expression of CD10, CD19, a lower percentage of CD20, minimal expression of CD22, and limited but polyclonal immunoglobulin light chain. Nine patients had received previous immunosuppressive therapy or BM transplantation or both, seven for hematolymphoid neoplasia. However, four patients with cytopenias of unknown etiology had no antecedent history of malignancy or marrow suppressive therapy. These findings demonstrate the clinical, morphologic, and immunophenotypic features of HGs in adults, and emphasize the difficulty in distinguishing these cells from residual marrow blasts after chemotherapy.