The antineoplastic, prodifferentiative effects of bromodomain and extra-terminal (BET) bromodomain (BRD) inhibitors were initially discovered in NUT midline carcinoma (NMC), an aggressive subtype of squamous cancer driven by the BRD4–NUT fusion oncoprotein. BRD4–NUT blocks differentiation and maintains tumor growth through a potent chromatin-modifying mechanism. OTX015/MK-8628, a novel oral BET inhibitor, targets BRD2/3/4/T with preclinical activity in NMC and several other tumor types and is currently in clinical development. Antitumor activity was evaluated in four patients with advanced-stage NMC with confirmed BRD4–NUT fusions who were treated with 80 mg OTX015/MK-8628 once daily in a compassionate-use context. Two patients responded rapidly with tumor regression and symptomatic relief, and a third had meaningful disease stabilization with a minor metabolic response. The main side effects were mild to moderate gastrointestinal toxicity and fatigue, and reversible grade 3 thrombocytopenia. This is the first proof-of-concept evidence of clinical activity of a BRD inhibitor in targeting BRD4–NUT. Significance: We present the first clinical proof-of-concept that targeting BRD4–NUT with a BET inhibitor results in impressive and rapid antitumor activity in NMC. It offers strong potential for future clinical application in this rare patient population as either a single agent or in combination with other agents.
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