Ambiguous phenotypes in acute leukemia

Several excellent reviews have been written on the phenomenon of ambiguous leukemic phenotypes, discussing their problematic interpretation and potential clinical significance.^1-5 The literature on this subject has introduced, supported or dismissed terms such as biphenotypia, mixed lineage and hybrid leukemias, lineage promiscuity and infidelity, all of which classify leukemic phenotypes outside the norm or not readily classifiable according to established systems. Controversial hypotheses have been formulated regarding the mechanisms leading to the coexpression of antigens from more than one cell lineage by single leukemic blast cells. One concept proposed a relationship between heterogenous leukemic phenotypes and normal, transient, primitive stages of hemopoietic differentiation. An alternative view suggested that acquired changes of a cell's genetic machinery could result in a deviation from its normal differentiation commitment.