PML/RAR alpha rearrangement in acute promyelocytic leukaemia with t(1;17) elucidated using fluorescence in situ hybridization

Acute promyelocytic leukaemia (APL) is characterized by t(15;17)(q22;q21) which results in the formation of two chimaeric genes, PML/RAR alpha and RAR alpha/PML, thought to play a role in leukaemogenesis. We report a case of a patient with APL apparently lacking the t(15;17) but with t(1;17) translocation identified by fluoresence in situ hybridization (FISH). Chromosome 15 seemed intact but PMI/RAR alpha fusion transcript was detected by molecular analysis. The patient achieved complete remission with all-trans retinoic acid treatment associated with chemotherapy. This case illustrates the usefulness of combined cytogenetics, FISH and molecular biology in cases with no evident t(15;17) to predict response to treatment.