- Patients included in this trial should have been diagnosed to have Acute Promyelocytic Leukemia morphologically on FAB criteria. This is sufficient to initiate therapy with arsenic tri-oxide but this diagnosis has to be confirmed using either Fluorescent in situ hybridization (FISH) for t(15;17) or reverse transcriptase polymerase chain reaction assay (RT-PCR) for PML-RARalpha transcripts within 7 days of inclusion into the study.