Immunohistochemical distinction of haematogones from B lymphoblastic leukaemia/lymphoma or B-cell acute lymphoblastic leukaemia (B-ALL) on bone marrow trephine biopsies: a study on 62 patients

Haematogones are normal, maturing B-cell precursors. They can be confused with neoplastic immature lymphoid cells of B lymphoblastic leukaemia/lymphoma or B-cell acute lymphoblastic leukaemia (B-ALL). Though multicolour flow-cytometry strategies for distinguishing haematogones from cells of B-ALL are well-described, similar strategies have not been determined for bone marrow trephine biopsies (BMTB). We revisited the morphological and immunohistochemical features (CD20, CD34, TdT and PAX5 expression) in 69 BMTB from 62 patients - 27 with excess haematogones; seven with residual B-ALL after therapy; 18 with no reported excess of haematogones or residual acute leukaemia on BMTB; and 17 diagnostic samples of B-ALL. The distinctive immunophenotypic pattern of BMTB with excess haematogones was of CD34, TdT, CD20 and PAX5 accounting for increasing proportions of cells in the order mentioned, whereas among B-ALL, the immunohistochemical pattern was of CD20, PAX5 and TdT accounting for an equal proportion of cells. Furthermore, among haematogones, the intensity of CD20 expression was extremely heterogeneous as compared to the neoplastic cells in CD20-positive B-ALL. The TdT-positive haematogones were generally small and uniform, while a certain degree of heterogeneity was noticed among neoplastic B-ALL cells. This study provides a practical strategy to distinguish haematogones from B-ALL cells in BMTB.