FHTX · Foghorn Therapeutics Inc.

This 8-K filing conveys high-materiality preclinical advancement across Foghorn’s core chromatin-targeting pipeline, anchored by compelling in vivo efficacy and mechanistic differentiation. The FHD-909 data — presented in collaboration with Lilly — go beyond standard monotherapy activity: the complete and durable regression with anti-PD1, coupled with failure of tumor re-implantation, strongly suggests induction of adaptive anti-tumor immunity, a feature rarely observed with targeted agents alone and one that could meaningfully enhance clinical utility in frontline SMARCA4-mutant NSCLC where immune checkpoint inhibitors currently underperform. The CBP degrader FHT-171’s robust activity in heavily pretreated ER+ breast cancer models addresses a high-burden, biomarker-defined population with limited options post-CDK4/6 inhibition, while its favorable tolerability profile mitigates a key risk for epigenetic degraders. Similarly, the EP300 degrader’s superiority over inobrodib — a dual CBP/EP300 inhibitor with known hematologic toxicity — in both efficacy and safety (including platelet preservation) positions it as a potentially best-in-class candidate for hematologic malignancies, particularly in resistant multiple myeloma. Finally, the demonstration of robust, orally viable ARID1B degradation validates Foghorn’s platform expansion into synthetic lethal targets previously considered undruggable, reinforcing the scalability of its Gene Traffic Control Platform®. Collectively, these data de-risk multiple parallel development paths, strengthen the scientific rationale for ongoing and planned IND-enabling studies, and reinforce the strategic value of the Lilly collaboration — especially given the $1.3 billion in potential milestones tied to the three undisclosed additional programs referenced in Exhibit 99.1.