A ferroptosis-suppressive tumor state to drive chemoradiotherapy resistance and define a therapeutic vulnerability in muscle-invasive bladder cancer.

195 Background: Bladder-preserving chemoradiotherapy (CRT) is a curative alternative to radical cystectomy for muscle-invasive bladder cancer (MIBC), yet durable disease control is limited by intrinsic resistance whose basis remains unclear. Methods: We performed transcriptomic profiling of pretreatment tumors from 179 patients uniformly treated with CRT and integrated gene expression with clinical outcomes, molecular subtype features, and immune contexture. Functional validation used CRT-resistant bladder cancer models and genome-wide CRISPR/Cas9 knockout screening under irradiation (IR). Results: We identified a ferroptosis-suppressive transcriptional signature (FSS) that defines a distinct resistance state and independently predicts radiographic progression-free and overall survival after CRT. High-FSS tumors showed inferior outcomes and were enriched for basal/squamous and immune-excluded phenotypes with reduced immune infiltration. This state was recapitulated in experimentally derived CRT-resistant models. CRISPR screening under IR identified core ferroptosis suppressor genes as essential survival dependencies and radiosensitizers, and pharmacologic ferroptosis induction restored radiosensitivity in resistant cells. Conclusions: A ferroptosis-suppressive state represents a mechanistically defined resistance program linking tumor-intrinsic transcriptional circuitry, immune microenvironment architecture, and therapeutic vulnerability. These findings establish ferroptosis regulation as a clinically actionable axis for risk stratification and therapeutic intensification in bladder-preserving MIBC. Multivariable Cox models evaluating clinicopathologic factors and FSS for radiographic progression-free survival. Multivariable Cox for rPFS HR (95% CI) P value Multivariable Cox for OS HR (95% CI) P value FSS High / Low 2.58 (1.64-4.05) &lt;0.001*** FSS High / Low 2.79 (1.66-4.67) &lt;0.001*** N1 / N0 2.44 (1.46-4.08) 0.001** LVI (+) / (-) 2.18 (1.14-4.16) 0.018* Ba/Sq / Others 2.06 (1.26-3.36) 0.004** With variant / pure UC 1.69 (0.89-3.19) 0.109 LVI (+) / (-) 1.71 (1.00-2.92) 0.048* N1 / N0 1.64 (0.92-2.95) 0.095 With variant / pure UC 1.52 (0.84-2.77) 0.168 Ba/Sq / Others 1.40 (0.82-2.40) 0.214 Grade high / low 1.38 (0.49-3.88) 0.539 cT stage &gt; T2 / &lt;T2 1.16 (0.70-1.92) 0.561 cT stage &gt; T2 / &lt;T2 1.33 (0.85-2.08) 0.219 Grade high / low 1.04 (0.33-3.30) 0.942 CIS (+) / (-) 0.57 (0.30-1.07) 0.081 Age ≥ 75 / &lt;75 0.70 (0.38-1.28) 0.245 Age ≥ 75 / &lt;75 0.55 (0.32-0.96) 0.036* CIS (+) / (-) 0.41 (0.18-0.97) 0.041* rPFS, radiographic progression-free survival; OS, overall survival (OS); HR, Hazard ratios; CI, confidence intervals; FSS, ferroptosis-suppressive signature; LVI, lymphovascular invasion; Ba/Sq, basal/squamous subtype; UC, urothelial carcinoma; CIS, carcinoma in situ. * P &lt; 0.05; ** P &lt; 0.01; *** P &lt; 0.001. </jats:t