Impact of BCR-ABL transcript type on outcome in patients with chronic-phase CML treated with tyrosine kinase inhibitors

The most common breakpoint cluster region gene-Abelson murine leukemia viral oncogene homolog 1 (BCR-ABL) transcripts in chronic myeloid leukemia (CML) are e13a2 (b2a2) and e14a2 (b3a2). The impact of the type of transcript on response and survival after initial treatment with different tyrosine kinase inhibitors is unknown. This study involved 481 patients with chronic phase CML expressing various BCR-ABL transcripts. Two hundred patients expressed e13a2 (42%), 196 (41%) expressed e14a2, and 85 (18%) expressed both transcripts. The proportion of patients with e13a2, e14a2, and both achieving complete cytogenetic response at 3 and 6 months was 59%, 67%, and 63% and 73%, 81%, and 82%, respectively, whereas major molecular response rates were 27%, 49%, and 50% at 3 months, 42%, 67%, and 70% at 6 months, and 55%, 83%, and 76% at 12 months, respectively. Median (international scale) levels of transcripts e13a2, e14a2, and both at 3 months were 0.2004, 0.056, and 0.0612 and at 6 months were 0.091, 0.0109, and 0.0130, respectively. In multivariate analysis, e14a2 and both predicted for optimal responses at 3, 6, and 12 months. The type of transcript also predicted for improved probability of event-free (P 5 .043; e14a2) and transformation-free survival (P 5 .04 for both). Compared to e13a2 transcripts, patients with e14a2 (alone or with coexpressed e13a2) achieved earlier and deeper responses, predicted for optimal European Leukemia Net (ELN) responses (at 3, 6, and 12 months) and predicted for longer event-free and transformation-free survival.