The impact of MRE11 in nuclear to cytoplasmic ratio on outcomes in muscle invasive bladder cancer an analysis of NRG/RTOG 8802, 8903, 9506, 9706, 9906, and 0233.

343 Background: Biomarkers are needed to help select patients (pts) with muscle invading bladder cancer (MIBC) for bladder sparing chemotherapy and radiation treatment (CRT). Higher MRE11 expression has been identified as a potential RT response marker in MIBC. MRE11 protein is involved in the DNA double strand break repair mechanism. This analysis evaluates associations between MRE11 expression and outcome in pts from 6 NRG/RTOG bladder-sparing RT protocols. Methods: Archival tissue via TMA or unstained slides was used. Cases were stained with anti MRE11 antibody Rabbit mAb, clone EPR3471 (Epitomics at 1:1500 dilution). Slides were scanned on an Aperio FL instrument and analyzed via Automated Quantitative Image analysis (AQUA). MRE11 scores were determined within the nucleus and cytoplasm of urothelial cells and a ratio of nuclear to cytoplasmic (N/C) score calculated. A ratio was used to normalize scores and overcome pre-analytical variation. MRE11 N/C was analyzed by quartile cut points. Cumulative incidence was used to estimate disease-specific mortality (DSM; failure=bladder cancer death) and Fine-Gray models were used to evaluate associations between MRE11 and DSM. Cox models were used for overall survival (OS; death) and bladder-intact survival (BIS; cystectomy/death). Results: Out of 465 eligible pts, tissue was available and MRE11 N/C determined for 135. Analyzable pts were less likely to be white (p=0.0001) and more likely to be T2 (p=0.0003). Median MRE11 N/C was 2.41 (min-max: 0.69-6.03). Pts with MRE11 N/C ≤ 1.49 (lower quartile) were associated with significantly higher DSM (HR= 2, 95% CI: 1.1, 3.8, p=0.03). The 4-year DSM was 41% for pts with MER11 N/C ≤ 1.49 vs. 21% for pts with MER11 N/C was >1.49. MRE11 N/C was not associated with OS or BIS. Conclusions: AQUA analysis allows precise measurement of this marker in tissue samples. Low expression of MRE11 N/C (≤1.49) is associated with significantly higher DSM. This adds further evidence of MRE11 as a potential RT response biomarker for selection of pts most likely to respond to bladder-sparing CRT. Supported by NCI grants U10CA180868, U10CA180822, UG1CA189867,U24CA196067.