We report the case of an 89-year-old male diagnosed with chronic-phase CML and expressing a rare e13a3 BCR-ABL1 fusion transcript. His cytogenetic analysis showed the t(9;22) translocation generating the Philadelphia chromosome (Ph), with a multiplex RT-PCR detecting an atypical fragment. Using two primers complementary to exon 10 of BCR and exon 4 of ABL1, a larger PCR product was observed, where after Sanger sequencing, an e13a3 BCR-ABL1 transcript was revealed. Given the diagnosis, the patient received 100 mg of dasatinib every other day and was then monitored by measuring both hematological and cytogenetic parameters, while his BCR-ABL1 transcripts were examined by PCR and semi-nested-PCR. According to the 2013 European Leukemia Network criteria, after six months of dasatinib the patient's response was classified as warning as he displayed 20% of Philadelphia-positive metaphases. Sequencing of the ABL1 catalytic domain did not detect point mutations. A complete cytogenetic response was achieved after one year of dasatinib. However, semi-nested-PCR confirmed the presence of the e13a3 BCR-ABL1 fusion transcript that has persisted up to the latest follow-up visit.The Philadelphia Chromosome (Ph) is generated by a reciprocal translocation t(9;22) (1, 2) leading to the assembly of a chimeric BCR-ABL1 oncogene that modulates the proliferation, apoptotic rate, cytoskeletal dynamics and microenvironment interaction of the hematopoietic stem cell, thereby giving rise to chronic myeloid leukemia (CML) (3-7). Usually, the BCR-ABL1 fusion encompasses exon 2 of the ABL1 gene that is fused in frame with one of three different breakpoints on the BCR gene: i) major (M-BCR), ii) minor (m-BCR) and iii) micro (μ-BCR). M-BCR includes the fusion transcripts in proximity of exons 13 or 14 of BCR, generating the more common e13a2 or e14a2 BCR-ABL1 variants. The remaining m-BCR and μ-BCR breakpoint clusters involve less common rearrangements affecting exons 1 or 19 of BCR that generate the e1a2 (8) or e19a2 fusions, respectively (9). Moreover, additional uncommon breakpoints have been previously described involving BCR exons 6 and 8 or ABL1 exon 3 (10). Interestingly, BCR-ABL1 isoforms involving exon 3 of ABL1 (e13a3, e14a3 and e19a3) have been described both in CML patients (11-13), with contrasting clinical outcomes, and in individuals diagnosed with Ph+ acute lymphoblastic leukemia ( 14). In the present study we report the case of a very elderly CML patient expressing a rare e13a3 BCR-ABL1 transcript displaying a partially satisfactory response to dasatinib (DAS) treatment.