A Case of Chronic Myeloid Leukemia with Micro BCR::ABL2 Rearrangement: Precaution in Reverse Transcription PCR to Prevent False Negativity

Abstract

We report a patient negative for BCR::ABL1 in qualitative reverse transcription (RT)-PCR but subsequently reported to be positive for t(9;22)(q34;q11.2) in conventional karyotyping. The patient was finally diagnosed with micro-type chronic myeloid leukemia after re-examining RT-PCR and performing targeted RNA sequencing. Through this case, we highlight the risk of false negativity when interpreting RT-PCR to detect micro-type fusion. Upon re-examining RT-PCR results, the patient’s internal control band was thicker than others. After extending the electrophoresis run time, a 911-bp internal control band and a target band around the level of 1.0 kb were separated. We confirmed a fusion breakpoint (BCR exon 19 and ABL1 exon 2) by targeted RNA sequencing, and it corresponds to 1,012 bp-sized e19a2 (c3a2) type among four micro-type fusion transcripts that RT-PCR HemaVision® kit M6B can detect.