Predictive Biomarkers and Personalized Medicine DNA Repair Biomarker Profiling of Head and Neck Cancer: Ku80 Expression Predicts Locoregional Failure and Death following Radiotherapy

Purpose: Radiotherapy plays an integral role in the treatment of head and neck squamous cell carcinoma (HNSCC). Although proteins involved in DNA repair may predict HNSCC response to radiotherapy, none has been validated in this context. We examined whether differential expression of double-strand DNA break (DSB) repair proteins in HNSCC, the chief mediators of DNA repair following irradiation, predict for treatment outcomes. Experimental Design: Archival HNSCC tumor specimens (n 1⁄4 89) were assembled onto a tissue microarray and stained with antibodies raised against 38 biomarkers. The biomarker set was enriched for proteins involved inDSB repair, in addition to establishedmechanistic markers of radioresistance. Staining was correlated with treatment response and survival alongside established clinical and pathologic covariates. Results were validated in an independent intramural cohort (n 1⁄4 34). Results: Ku80, a key mediator of DSB repair, correlated most closely with clinical outcomes. Ku80 was overexpressed in half of all tumors, and its expression was independent of all other covariates examined. Ku80 overexpression was an independent predictor for both locoregional failure and mortality following radiotherapy (P < 0.01). The predictive power of Ku80 overexpressionwas confined largely toHPV-negative HNSCC, where it conferred a nine-fold greater risk of death at two years. Conclusions: Ku80 overexpression is a common feature of HNSCC, and is a candidate DNA repairrelated biomarker for radiation treatment failure and death, particularly in patients with high-risk HPVnegative disease. It is a promising, mechanistically rational biomarker to select individual HPV-negative HNSCC patients for strategies to intensify treatment. Clin Cancer Res; 17(7); 2035–43. 2011 AACR.