Masked t(15;17) APL with the insertion of PML-RARα fusion gene in 4q21

Most cases of acute promyelocytic leukemia (APL) are characterized by the reciprocal translocation t(15;17); however, several complex variant translocations have also been reported. Here we report complex cytogenetic abnormalities without t(15;17) assayed by the G-banding method in a 62-year-old woman with the typical morphology and clinical features of APL. Based on spectral karyotyping and FISH analyses, we confirm the insertion of a cryptic chromosomal segment containing the PML/RARα fusion gene. The patient achieved complete remission after treatment with all-trans retinoic acid (ATRA) alone. Although the mechanism of this cryptic variant insertion is not known, we conclude that the insertion of PML-RARα fusion into 4q21 seems not to alter the effectiveness of treatment with ATRA.