B-MYB (MYBL2): from cell cycle regulator to an oncogenic player.

B-MYB (MYBL2) is a transcription factor of the MYB family that plays critical roles in cell cycle progression, proliferation, and survival. Through the DREAM-MMB-FOXM1 network, B-MYB coordinates the expression of genes required for mitosis and cytokinesis (G2/M genes), while genes required for DNA replication during S phase are regulated by E2F-DP complexes. Initially identified as a regulator of normal cell cycle processes, B-MYB has emerged as a key oncogenic driver across multiple cancer types. This review addresses the physiological roles of B-MYB, the mechanisms underlying its oncogenic activation, and its contributions to tumorigenesis and clinical relevance as a prognostic biomarker and potential therapeutic target. Aberrant activation of B-MYB, driven by gene amplification, transcriptional upregulation, or post-translational modification, is reported as a recurrent feature of aggressive cancers. The consequences of B-MYB overexpression, including uncontrolled proliferation, genomic instability, apoptosis evasion, epithelial-to-mesenchymal transition, therapy resistance and metabolic reprogramming, further underscore B-MYB as a central oncogenic driver. Clinically, B-MYB overexpression correlates with poor prognosis, advanced disease and chemoresistance across multiple malignancies. Thus, we aim to emphasise the biological roles of B-MYB in physiological and cancer mechanisms, alongside the growing evidence establishing it as both a biomarker of disease and a potential therapeutic target. While previous reviews have addressed isolated aspects of B-MYB biology, this review provides a comprehensive and updated integration of recent mechanistic advances (A-MYB/B-MYB functional redundancy and YAP/TAZ-TEAD crosstalk) and the therapeutic potential of non-canonical DNA structures at the B-MYB promoter. We further review current trends and methodologies for targeting B-MYB and outline new perspectives for future therapeutic research.