Typical acute promyelocytic leukemia (APL) is associated with the t(15;17) translocation, expression of a PML/RARA fusion transcript, and responsiveness to all-trans retinoic acid (ATRA). Rare APL cases implicating the RARA but not the PML gene have been reported. Cases with t(11;17)(q23;q21) which fuses the PLZF and RARA genes do not respond to ATRA. In contrast, cases with t(11;17)(q13;q21) and t(5;17)(q35;q21) which fuse RARA with NuMA and NPM, respectively, were reported to be sensitive to ATRA. We described previously an APL case with an unbalanced t(5;17) implicating RARA but neither PML nor PLZF. Here, we show that in this case: (1) the NPM gene is not involved, as demonstrated by RT-PCR and Southern blot; (2) response to ATRA in vitro is atypical, as demonstrated by morphological and functional maturation assays; and (3) PML nuclear bodies are not disrupted, as evidenced by immunofluorescence staining.