Primary resistances to EGFR inhibitors (EGFRi) in HPV-positive and -negative oropharyngeal squamous cell carcinoma (OSCC).

10591 Background: HPV-positive and negative OSCC, despite a common EGFR expression, have a distinct biology and clinical behaviour, thus we hypothesize different mechanisms of primary resistance to EGFRi. Methods: PI3KCA, PTEN, HER2 and IGF-1R status was investigated in 17 HPV16-positive and 57 HPV16-negative fixed untreated OSCCs through FISH, sequencing, cDNA relative quantification by means of real-time PCR (method 2-ΔΔCt) and immunohistochemistry. Results: PI3KCA gene amplification involved only HPV16-negative (13%) cases, while a gain of PI3KCA gene copy number similarly occurred in HPV16-positive (29%) and negative (25%) OSCC. Activating mutations play a marginal role both in HPV16-positive (6%) and negative (2%) OSCC. An higher occurrence of PI3KCA transcript values, 31 folds > than the lower one, was found in HPV16-positive (60%) compared with negative (27%) OSCC (p=0.05). PTEN gene loss was restricted to HPV16-positive (12%) cases, while PTEN mutation similarly involved both HPV16-positive (9%) a...