Karyotype evolution in a patient with biphenotypic neonatal leukemia.

We present the case of a 4-day-old boy with acute lymphoblastic leukemia showing at onset a karyotype 46,XY,t(4;11)(q21;q23). At relapse an additional change, add(2), was present. Molecular analysis showed the same immunoglobulin rearrangement both at onset and at relapse, but immunohistochemical analysis revealed some cells having myeloid features. A continuous cell line derived from the leukemic blasts of the patient presented typical monoblastic features.