SHORT REPORT Congenital leukaemia with a mixed phenotype of megakaryoblasts and erythroblasts: a case report and characterization of the blasts T ETSUYA MORI ,H IDEO K ANEKO,* MASA- AKI K UMAGAI ,J UN MIYAUCHI ,† YASUHIKO K ANEKO,‡ J UNICHIRO F UJIMOTO * AND Y UKIKO T SUNEMATSU Department of Haematology and Oncology, †Department of Pathology, National Children’s Hospital, *Department of Pathology, National Children’s Medical Research Centre, Setagaya-ku, Tokyo, and ‡Department of Cancer Chemotherapy, Saitama Cancer Centre Hospital, Saitama, Japan Received 21 November 1996; accepted for publication 29 November 1996 Summary. We present a congenital leukaemia with a mixed phenotype of megakaryoblasts and erythroblasts. A new- born male with exopthalmus and multiple skin nodules, had bone marrow blasts which expressed CD41b, CD42b, glycophorin-A and haemoglobin, but monocyte or lym- phoid markers were negative. The patient achieved a complete remission with chemotherapy. Blasts cultured for a few months expressed erythroid markers but lost the megakaryocytic phenotype, although addition of phorbol ester induced the latter phenotype. Spontaneous colony formation was observed in semi-solid culture and the number of colonies was increased by erythropoietin. Detailed studies further indicated the heterogeneity of congenital leukaemia. Keywords: congenital mixed leukaemia, mixed phenotype. CASE REPORT A male baby was delivered at 39 weeks gestation who had an extrusion of the right opthalmus and multiple skin nodules. Bone marrow examination revealed an extensive blast population. Morphologically, the blasts were large in size, irregular in shape and had basophilic cytoplasm with vacuoles. Myeloperoxidase, alpha-naphtyl-butyrate-esterase and PAS staining were all negative but acid phosphatase was partially positive. The blasts could not be classified into suitable FAB criteria by morphology and special staining. However, the blasts simultaneously expressed the mega- karyocyte (CD41b and CD42b) and erythrocyte markers (glycophorin A (GPA) and haemoglobin) (Table I). Myeloid markers (CD11b, CD13 and CD33) were weakly expressed by the blasts but monocyte markers (CD14, alpha-1-antitrypsin and lysozyme) and lymphoid markers (CD1, CD2, CD3, CD4, CD5, CD19, CD20 and CD22) were completely negative. By electron microscopy, the blasts showed platelet peroxidase reaction (PPO). A biopsied skin nodule showed an infiltration of cells with a similar immunophenotype in the dermis. No chromosomal abnormality in the mitotic figures prepared from bone marrow and no congenital anomalies by physical examination ruled out the possibility of pro- liferation of megakaryoblasts occasionally seen in Down’s syndrome. MLL gene rearrangement was not detected by Southern blot analysis. Radiological examination indicated the infiltration of the blasts into multiple organs including skull, subcutaneous tissue of the scalp, right lower lobe of the lung, liver and spleen. The diagnosis of congenital leukaemia with a mixed phenotype of megakaryoblasts and erythroblasts was made based on these data. The general condition of the patient was fairly good but chemotherapy (etoposide, cytarabin and mitoxantrone) was started when he was 10 d old because the number of skin nodules increased and exophthalmus progressed. Response to this treatment was remarkable and the exophthalmus, skin tumours and hepatosplenomegaly almost completely disappeared 5d after the initiation of therapy. Complete haematological remission was con- firmed on day 53 and infiltration of the leukaemic cells in organs disappeared as confirmed by computed tomography. The patient has grown normally to date and no sign of relapse was apparent at the age of 14 months at the time of writing. British Journal of Haematology , 1997, 96, 740–742 740  1997 Blackwell Science Ltd Correspondence: Dr Junichiro Fujimoto, Department of Pathology, National Children’s Medical Research Centre, 3-35-31 Taishido, Setagaya-ku, Tokyo, 154, Japan.