Cryptic t(15;17) acute promyelocytic leukemia with a karyotype of add(11)(p15) and t(13;20) - A case report with a literature review

Most acute promyelocytic leukemias (APL) are characterized by reciprocal translocations t(1.537)(q22;21), which results in the fusion of the promyelocytic leukemia protein (PML) gene at 15q22 with retinoic acid receptor alpha (RAR alpha ) gene at 17q21. However, several complex variant translocations also have been reported. Here, we report a 62-year-old man with typical morphology and clinical features of APL with a complex karyotype including add(u)(pis) and t(13;20)(q12;q11.2) without typical t(15;17) assayed by the G-banding analysis. The fluorescence in situ hybridization with a PML/RAR alpha dual-color DNA probe showed an atypical fusion signal, quantitative real-time polymerase chain reaction analysis showed PML/RAR alpha fusion transcripts, and NGS detected FLT3, WT1, and KRAS mutations. The patient achieved complete remission after treatment with conventional chemotherapy combined with all-trans retinoic acid (ATRA) and arsenic trioxide (ATO). Although the mechanism of this kind of cryptic variant remains unknown, we conclude that the cryptic PML/RAR alpha fusion with add(u)(pis) and t(13;20) (q12;q11.2) seems not to alter the effectiveness of chemotherapy combined with ATRA and ATO.