Prevalence and outcomes of uncommon BCR‐ABL1 fusion transcripts in patients with chronic myeloid leukaemia: data from a single centre

To explore the type, prevalence and outcomes in chronic myeloid leukaemia (CML) patients with uncommon BCR-ABL1 transcripts in the era of tyrosine kinase inhibitors (TKIs), uncommon BCR-ABL1 transcripts were screened in 4750 patients by multiplex polymerase chain reaction (PCR), and type-specific real-time quantitative PCR was regularly performed for molecular monitoring. A total of 19 uncommon transcripts, including e1a2, e1a3, e6a2, e8a2, e12a2, unusual e13a2, e13a3, unusual e14a2, e14a3 and e19a2 were identified in 83 (1·7%) patients. The three most frequent types were e19a2, e13a3/e14a3 and e1a2. Compared with the 571 newly diagnosed CML patients in chronic phase with common e13a2/e14a2 transcripts receiving frontline imatinib therapy, patients with the e19a2 (n = 16) and e1a2 (n = 11) transcripts had significantly reduced probabilities of 1-year complete cytogenetic response (CCyR, P = 0·0004 and 0·016) and major molecular response (MMR, P = 0·0018 and 0·0035), and patients with the e13a3/e14a3 transcript (n = 10) had significantly increased probabilities of 1-year CCyR (P = 0·0072) and MMR (P = 0·0073). Patients with the e19a2 transcript had low probabilities of 2-year event-free survival (EFS, P = 0·0004) and progression-free survival (P = 0·0067), and patients with the e1a2 transcript had low probability of 2-year EFS (P < 0·0001). Therefore, uncommon BCR-ABL1 fusion transcripts are rare and diverse in patients with CML and may be relevant for TKI therapy outcomes.