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6061 Background: Platinum-based chemotherapy in association to cetuximab is the standart first-line treatment for metastatic HNSCC. There is no established biomarker for cetuximab efficacy in HNSCC. We have previously shown that PTEN loss of expression is a bad prognostic factor for patients treated with platinum-based chemotherapy and cetuximab. The aim of the present study was evaluate the prognostic impact of PTEN loss of expression in patients treated with or without cetuximab and to evaluate its predictive value to cetuximab benefit. Methods: One hundred and nineteen patients with metastatic or locally recurrent HNSCC were included. Clinical data on treatment and outcomes was retroespectively colected from medical charts. Tissue micro-array was constructed to evaluate PTEN protein expression through immunohistochemistry. Citoplasmatic staining was evaluated using H-score. Tumors with H-score < 10 were considered to present PTEN loss of expression. Results: From the 119 patients 72 were treated with chemotherapy plus cetuximab while 47 were treated with chemotherapy alone. Median overall survival (mOS) was 9.2 months and median progression free survival (PFS) was 4.6 months. Patients treated with cetuximab compared to those who were not treated with cetuximab had a mOS of 11.4 vs 7.0 months (p = 0.770) and a median PFS of 6.2 vs 3.0 months (p = 0.249). Patients with PTEN loss of expression had a worse OS and PFS with mOS of 5.8 vs 10.5 months (p = 0.002) months and mPFS of 3.2 vs 5.2 (p = 0.015). On multivariate analysis including PTEN loss of expression and ECOG performance status both remained independently associated to survival with HR 2.25 (CI95% 1.28-3.97, p = 0.005) for PTEN loss of expression and a HR 1.63 (CI95% 1.07-2.50, p = 0.023) for ECOG. Negative prognostic impact of PTEN loss of expression was seen only in the cetuximab treated patients (mOS 7.3 vs 13.0 months; p = 0.002) but not in the chemotherapy only group (mOS 3.2 vs 7.5 months; p = 0.051). Interaction test for treatment group and PTEN loss of expression showed a p = 0.418. Conclusions: The present study confirms PTEN as a prognostic factor for metastatic HNSCC and suggests PTEN expression should be studied in larger cohorts to evaluate its predictive value to cetuximab response.

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