Inhibition of Bromodomain and Extra-Terminal Domain Proteins in Solid Tumors: Advances, Challenges, and Future Directions

The bromodomain and extra-terminal domain (BET) protein family, particularly BRD4, is critical for the control of oncogenic transcriptional programs in solid tumors. Although initial-generation BET inhibitors, such as JQ1, molibresib, and birabresib, have demonstrated preclinical efficacy in repressing MYC-dependent pathways, their clinical translation has been hampered by low monotherapy activity, pharmacokinetic heterogeneity, and dose-limiting toxicities. This review aims to update the mechanistic foundations, clinical trial results, and development of therapeutic approaches to BET inhibition in solid tumors, outlining its evolving role in the next generation of cancer treatment strategies. Various clinical trials in different phases have demonstrated heterogeneous responses among solid tumor types, with greater effects in NUT carcinoma and castration-resistant prostate cancer. Resistance mechanisms, including BRD4 isoform switching and compensatory signaling activation, emphasize the need for advanced and innovative BET-targeting modalities. BD2-selective BET inhibitors and proteolysis-targeting chimeras are likely to overcome these limitations by increasing target specificity and reducing systemic side effects. In addition, combination strategies, such as PARP inhibitors, AR antagonists, and immune checkpoint blockade, have synergistic potential to augment anticancer activity. In conclusion, this review provides a comprehensive overview of the advances, challenges, and future directions of BET bromodomain inhibition in solid tumors.