(3) APL is not a homogeneous disease in that among 50 patients studied at the molecular level, although a PML-RARA fusion gene was detected in 45 cases, one had a variant translocation t(11;17) bearing fusion gene PLZF-RARA, one presented no obvious structural alteration of the PML gene while the RARA gene was rearranged, and three patients had no rearrangement of either PML or RARA genes.     ///    (5) It seems likely that the fusion gene PML-RARA plays an important role in APL leukemogenesis and in its response to the ATRA treatment.. 