FISH Signal Pattern for an APL Variant Translocation with a PRKAR1A-RARA Fusion

Fluorescence in situ hybridization (FISH) is a quick and reliable test to detect the reciprocal t(15;17)(q22;q21) translocation in acute promyeloid leukemia (APL). The typical signal pattern for positive t(15;17) is one red, one green, and two fusion when using a PML/RARA dual fusion translocation probe. However, for variant translocations leading to the fusion of a RARA gene with an alternate gene partner, a RARA break-apart probe should be used to verify the RARA rearrangement. The typical signal pattern for a positive RARA break-apart probe is one red, one green, and one fusion. In this study, we report a rare APL case with a PRKAR1A-RARA fusion gene with a signal pattern distinct from that of t(15;17) and its other variants.