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Detection and Clinical Implications of a Novel BCR-ABL1 E12A2 Insertion/Deletion in a CML Patient Expressing the E13A2 Isoform

Background/Aim: The Philadelphia chromosome is the most frequent cytogenetic abnormality in chronic myelogenous (CML). More than 95% of CML patients are diagnosed with the e13a2 or e14a2 BCR-ABL1 fusion transcripts while, in about 1% of these individuals, the break generates the e1a2 rearrangement. Furthermore, about 5% of CML patients are diagnosed with rare BCR-ABL1 fusion transcripts, such as e19a2, e8a2, e13a3, e14a3, e1a3 and e6a2. However, there is limited evidence concerning the clinical and prognostic implications of these infrequent oncogenic variants for CML patients receiving tyrosine kinase inhibitors (TKIs). Case Report: We describe a novel atypical e12a2 insertion/deletion (Ins/Del) BCR-ABL1 fusion identified in a CML 59-year-old man diagnosed with a common e13a2 BCR-ABL1 isoform. The use of primers recognizing more distant exons from the common BCR-ABL1 breakpoint region correctly identified and monitored in time the atypical e12a2 Ins/Del BCR-ABL1 fusion. Conclusion: Treatment with second- (nilotinib) and third-generation (ponatinib) TKIs was effective in suppressing leukemic clones exhibiting the atypical e12a2 Ins/Del BCR-ABL1.