Simultaneous occurrence of acute monoblastic leukemia and an abnormal B‐cell clone with both cell types characterized by specific cytogenetic and immunological markers

2 different, unrelated, abnormal clones of cells were found in a patient with acute leukemia, each clone being characterized by specific cytogenetic abnormalities and a distinct immunological phenotype. Bone marrow morphology and cytochemistry indicated an acute monoblastic leukemia, a diagnosis supported by the finding of a t(9;11) in bone marrow cells. In PHA-stimulated blood culture, another abnormal karyotype was found in 16% of the metaphases: 47, XY, +12, inv(13), t(14;18). Immunologically, the blood contained 3 types of mononucleated cells (MNC): 1) large cells (about 70% of the MNC) with a phenotype consistent with monoblastic/monocytic leukemic cells (My7+, My8+, My906+, My4+, Leu-M3+); 2) small lymphocytic cells with either T-cell characteristics (6% of the MNC); or 3) B-cell monoclonal features (24% of the MNC). The monoclonal B-cell population was Sm K+, μ +, δ+, BA-1+, B1+, Y29/55+ and FMC7+. The possible origin of this abnormal (malignant) B-cell population is discussed. However, this B-cell clone was clinically silent and the patient' death precluded further observations.