Acute leukemia with t(10;11)(p11-p15;q13-q23).

We report six patients with acute leukemia characterized by the presence of a t(10;11)(p11-15;q13-q23), either as sole cytogenetic abnormality (three patients) or as part of a complex abnormal karyotype. The morphologic and cytochemical features of four patients were consistent with FAB-M5A, while two patients presented with FAB-L1 characteristics. By immunophenotyping, myeloid leukemia was diagnosed in five patients, including one patient with FAB-L1 leukemia who typed as terminal transferase (TdT)+, CD7 T-cell antigen+ acute myelomonocytic leukemia. Differentiated acute myeloid leukemia (AML) with expression of terminal transferase was found in two of the other cases and monocytic leukemia in two, with co-expression of T-cell antigens in one of them. The second FAB-L1 patient typed as undifferentiated acute lymphocytic leukemia (ALL) expressing myeloid antigens. Serial phenotypic studies in patient 3 during the course of the disease demonstrated a switch from monocytic to lymphoid morphology at the time of first and second relapse, which was paralleled by the appearance of a pre-T ALL immunophenotype with co-expression of the myeloid antigen CD33. These phenotypic changes occurred without apparent alteration in the genotype since t(10;11)(p11.2;q23) remained the only cytogenetic aberration at all stages of the disease. Our observations suggest that the (10;11) variant of 11q aberrations occurs in a bipotential myelomonocytic/T-lymphoid stem cell.