Non-neoplastic TdT-positive cells in bone marrow trephines with acute myeloid leukaemia before and after treatment express myeloid molecules.

OBJECTIVES Terminal deoxynucleotidyltransferase (TdT)-positive cells in non-neoplastic bone marrow are regarded as haematogones and show a characteristic morphology and immunophenotype. During our routine bone marrow trephine analysis of patients with acute myeloid leukaemia (AML) before and after treatment, we observed the presence of TdT-positive cells lacking CD34, CD10 and B cell antigens. METHODS To verify the nature of these TdT-positive cells, we analyzed 140 paraffin-embedded and decalcified trephines from 67 AML patients before and after therapy using double immunolabellings. RESULTS In 61% of the cases TdT-positive cells were present. After exclusion of neoplastic cells and haematogones, we identified that 16% of the cases harboured cells co-expressing myeloperoxidase and TdT, 15% glycophorin C and TdT, 13% CD117 and TdT and one case CD3 and TdT. These cells made up to 30% of the non-neoplastic TdT-positive cells. No differences in the number of TdT-positive cells before and after chemotherapy or stem cell transplantation could be observed. CONCLUSION While the reason of TdT expression by non-neoplastic myeloid cells is unknown, their presence should be taken into account when evaluating such cases.