Breakpoint cluster region–Abelson murine leukemia viral oncogene fusion kinase (BCR-ABL1 (also BCR-ABL))

The **Breakpoint cluster region–Abelson murine leukemia viral oncogene fusion kinase (BCR-ABL1)** is an oncogenic fusion protein generated by the t(9;22)(q34;q11) chromosomal translocation, known as the Philadelphia chromosome, resulting in the fusion of the BCR gene on chromosome 22 and the ABL1 gene on chromosome 9[3][4][5]. The most common variants are p210 BCR-ABL (found in chronic myeloid leukemia, CML), p190 BCR-ABL (acute lymphoblastic leukemia, ALL), and p230 BCR-ABL (rare, chronic neutrophilic leukemia)[3]. BCR-ABL1 is a constitutively active **tyrosine kinase** that promotes cell proliferation, survival, and malignant transformation by phosphorylating itself and multiple downstream substrates (notably STAT5, CrkL), thereby activating aberrant cell signaling cascades[3][4][6]. The loss of the ABL1 N-terminal autoinhibitory cap domain and its replacement by BCR-derived oligomerization domains results in persistent kinase activation and loss of normal regulatory control[1][4][5]. This leads to uncontrolled expansion of leukemic cells with impaired apoptosis and altered cell adhesion. BCR-ABL1 is a **critical therapeutic target**: inhibition with tyrosine kinase inhibitors (TKIs) such as imatinib, dasatinib, nilotinib, bosutinib, and ponatinib is highly effective and forms the basis of frontline therapy in CML and Ph+ ALL[7]. Resistance can develop through kinase domain mutations (especially T315I), requiring alternative therapies or newer inhibitors with distinct binding properties[7]. **Diagnosis and disease monitoring** rely on sensitive PCR-based detection of BCR-ABL fusion transcripts, and quantitative measurement of BCR-ABL mRNA levels is used as a biomarker to assess therapeutic response and predict relapse. The presence of the Philadelphia chromosome remains a fundamental diagnostic hallmark[3][5]. Safety concerns include resistance mutation development, off-target effects, and adverse event profiles specific to each inhibitor[7]. The BCR-ABL1 fusion kinase remains one of the most studied and clinically actionable molecular targets in hematologic oncology[3][4][5][7].

Other names

Philadelphia chromosome fusion proteinBCR-ABL fusion proteinBCR::ABL1BCR-ABL tyrosine kinaseBCR-ABL1 fusion proteinp210 BCR-ABLp190 BCR-ABLp230 BCR-ABL

Competitive inhibition of the ATP-binding site of BCR-ABL kinase; Allosteric inhibition (asciminib); Inhibition of autophosphorylation; Inhibition of downstream signaling (e.g., STAT5 inactivation)