P16 Expression As A Human Papillomavirus (Hpv)-Independent Prognostic Biomarker In Non-Oropharyngeal Squamous Cell Carcinoma (Non-Opscc)

6007 Background: p16 is an important tumor suppressor and cell cycle regulator that is commonly lost in HPV-negative (-) and upregulated in HPV-positive (+) OPSCC. While the role of p16 expression in OPSCC as a surrogate marker of HPV infection and its association with prognosis are well established, its significance has not been studied in non-OPSCC including oral cavity, hypopharynx and larynx, where HPV infection is rare. We hypothesize that p16 expression is a prognostic biomarker of favorable outcome (progression-free and overall survival) in non-OPSCC. Methods: p16 expression in non-OPSCC from RTOG 0129, 0234 and 0522 was determined by immunohistochemistry (p16 mouse monoclonal antibody, prediluted, MTM-CINtech, 9518) and considered positive if >70% of the tumor cells demonstrated diffuse staining. The high risk HPV status in non-OPSCC from RTOG 0129 and 0522 was determined by in situ hybridization using a cocktail probe including HPV16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58 and 66. Hazard ratios from Cox models were expressed as positive/negative, stratified by trial, and adjusted for age, gender, T, and N stage. Results: p16 expression was positive in 14.1% (12/85), 24.2% (23/95) and 19.0% (27/142) of non-OPSCC from RTOG 0129, RTOG 0234, and RTOG 0522, respectively. HPV ISH was positive in 6.5% (6/93) and 6.9% (7/101) of non-OPSCC from RTOG 0129 and RTOG 0522, respectively. There was moderate agreement between p16 and HPV status (kappa=0.53). The hazard ratios for p16 expression are 0.63 (p=0.03) and 0.56 (p=0.01) for PFS and OS, respectively. In 0522, there was no interaction between p16 status and two treatment arms (RT+cisplatin+/-cetuximab). In comparison of OPSCC and non-OPSCC, patients with p16(+) OPSCC have better PFS and OS than patients with p16(+) non-OPSCC, but patients with p16(-) OPSCC and non-OPSCC have similar outcomes. Conclusions: Similar to results in patients with OPSCC, patients with p16(+) non-OPSCC have better outcomes than patients with p16(-); however, the differential appears smaller than has been observed in HPV(+) OPSCC. Further studies are warranted to delineate the role of p16 expression as a prognostic biomarker in non-OPSCC and OPSCC. Clinical trial information: NCT00265941, NCT00047008, NCT00084318.