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Prostate cancer is driven by oncogenic transcription factor enhanceosomes comprising chromatin and epigenetic regulators. The lysine acetyltransferases p300 and CREB-binding protein (CBP) are key cofactors that activate enhancers through histone acetylation. Here we identify p300/CBP-mediated multisite histone H2B N-terminal acetylation (H2BNTac) as a defining feature of oncogenic enhanceosomes in androgen receptor (AR)-positive prostate cancer. p300/CBP are essential for AR and ETS transcription factor ERG transcriptional activity, and their dual degradation eliminates H2BNTac and histone H3 lysine 27 acetylation at hyperactive enhancers, leading to stronger suppression of oncogenic transcription than targeting either paralog or bromodomain alone. Cytotoxicity profiling across >900 cell lines revealed that tumors with high H2BNTac, including AR-positive prostate cancer, are selectively dependent on p300/CBP. In preclinical models, systemic p300/CBP degradation inhibited tumor growth, synergized with AR antagonists and showed no evident toxicity. These findings position H2BNTac as an epigenetic marker of enhancer addiction and establish dual p300/CBP degradation as a promising therapeutic strategy for enhancer-driven cancers.