Differences in biomarker expression in HNSCC according to p53 status.

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5523 Background: Patients with p53 wildtype head and neck squamous cell carcinoma (HNSCC) tend to be HPV-positive, which associates with better prognosis. The purpose of this study was to explore biomarker expression profiles for insight into molecular differences in HNSCC patients based on p53 status. Methods: TP53 gene sequencing using the AmpliChip p53 microarray (Roche Molecular Systems, Inc.) was attempted on 61 HNSCC patients previously tested with Caris Target Now tumor profiling service. DNA was extracted from a FFPE sample, amplified and processed on the AmpliChip p53 microarray to detect single base pair substitution and deletion mutations in exons 2 - 11 and their flanking splice sites in the TP53 gene (GenBank X54156). EGFR FISH , HER2 IHC and 22 other predictive biomarkers, e.g. TS, TOPO2A, MGMT, etc., were assayed and retrospectively analyzed. All tests were performed in a CLIA-certified lab and interpreted by board-certified pathologists or cytogeneticists. Statistical analysis was performed using SPSS (PASW statistics17) for parametric and non-parametric tests of independence. Results: 52 cases provided sufficient quality DNA for p53 analysis and results revealed a mutation rate of 25% in HNSCC patients. Interestingly, only EGFR FISH and HER2 IHC (p=.002 and p=.004, respectively) were differentially expressed in wildtype vs. mutated p53. Matched-pair analysis in the p53 mutated subgroup (n=13) showed no significant trend regarding EGFR status (p=.763) but a slight trend towards HER-2 negativity (p=.020). In the p53 wildtype subgroup (n=39), a strong association with EGFR FISH non-amplification (n=28, 71.8%, p<.001) as well as HER-2 negativity (n=38, 97.4%, p<.001) was shown. Conclusions: To our knowledge, this is the first analysis of differential biomarker expression profiles in HNSCC based on p53 status. We hypothesize that the absence of EGFR amplification in the p53 wildtype cancers may be a contributing factor to the improved prognosis observed in HPV-positive HNSCC. Additionally, the strong association between p53 wildtype HNSCC patients and EGFR non-amplification suggests EGFR-targeted therapies like cetuximab would likely fail in p53 wildtype patients.