Aberrant positivity for CD79a in erythroid lineage cells a finding observed in a subset of re-staging bone marrow trephine biopsies after treatment

* London, UK & Department of Haematology, Ealing Hospital, London, UK ° Department of Histopathology, Hammersmith Hospital and Imperial College Correspondence: Professor Kikkeri N. Naresh, Haematopathologist, Department of Histopathology, Hammersmith Hospital & Imperial College, Du Cane Road W12 0HS, London, UK. Phone: international +44.020. 83833969. Fax: international +44.020.8383 3140. E-mail: k.naresh{at}imperial.ac.uk Aberrant expression of CD79a has been reported in neoplastic cells in peripheral T cell lymphoma, T-cell acute lymphoblastic leukemia and acute myeloid leukemia (especially those with t(8;21)). In this report, we document the first report of CD79a positivity in erythroid precursor cells in bone marrow. In all, we document this finding in five of 18 re-staging bone marrow trephine samples in patients of lymphoma treated with chemotherapy (one index case and 17 additional validation cases). It is important to appreciate this finding especially in rituximab treated patients where one tends to rely on CD79a to identify minimal marrow disease.