Targeting the YAP-mediated stromal signaling unlocks chemoresistance in a human organoid fibrosis model.

The fibrotic stroma drives tumor progression and impairs therapy, but existing models fail to capture its dual barrier and signaling roles, limiting mechanistic understanding and therapeutic development. To address this, we established a patient-derived fibrotic tumor model that recapitulates key pathophysiological features: extracellular matrix remodeling, substantial tissue stiffening (12-fold increase), and pro-malignant transcriptomic reprogramming. This model demonstrated microenvironment-mediated chemoresistance, increasing the area under the dose-response curve by 1.3-fold and suppressing oxaliplatin-induced apoptosis. Although stiffening delayed drug penetration, barrier disruption did not restore sensitivity. Instead, stiffness inactivated the Hippo pathway, activating YAP as the key chemoprotection driver. YAP inhibition restored drug sensitivity without altering stiffness, revealing a targetable biochemical mechanism independent of the physical barrier. Using this insight, we designed a sequential regimen in which nintedanib preconditioning precedes chemotherapy, achieving near-complete tumor eradication (<5% tumor viability). This work provides a physiological model of stromal biology and a mechanism-guided strategy to overcome microenvironment-mediated chemoresistance.