FISH Detection ofPML-RARAFusion in ins(15;17) Acute Promyelocytic Leukaemia Depends on Probe Size

Abstract

The diagnosis of acute promyelocytic leukaemia (APL) is usually confirmed by cytogenetics showing the characteristic t(15;17), but a minority of patients have a maskedPML/RARAfusion. We report ten patients with APL and no evidence of the t(15;17), in whom the insertion ofRARAintoPMLcould not be demonstrated by initial FISH studies using a standard dual fusion probe but was readily identified using smaller probes. Given the need for rapid diagnosis of APL, it is important to be aware of the false negative rate for largePML/RARAFISH probes in the setting of masked rearrangements.