Genetic alterations in HRAS gene in relation to outcome and response to cetuximab in head and neck squamous cell carcinoma.

Abstract

5574 Background: Aberrant signaling through RAS/MAPK pathway is implicated in resistance to EGFR-targeted agents in cancer. Genetic alterations in Hras gene such as mutations and specific polymorphisms are associated with aggressive phenotype in several smoking-related malignancies. We sought to determine the impact of Hras genetic alterations on response to cetuximab and prognosis in HNSCC. Methods: Clinical outcome according to Hras status was investigated in a retrospective cohort of 140 HNSCC specimens. Primary endpoints were overall survival (OS) and disease-free survival (DFS) and secondary endpoint was treatment response. For statistical analysis, T-test was used for continuous data and x2 –test for categorical data. Cetuximab-resistant cell lines harboring mutant Hras (BB49, T24) were infected with lentivirus expressing shRNA targeting the Hras or a scrambled- shRNA. MTT assay was used to determine the effect of cetuximab on growth of lentivirus infected cells. Biochemical analysis involved immunoblotting for pERK1/2. Results: Mutationanalysis of tumor samples showed that 5.7% participants harbored Hras mutations and 16.42% harbored Hras polymorphisms (rs12628, rs41258054) that are associated with tumorigenesis. Patients bearing tumors with mutated Hras had inferior mean OS ( 22.13vs 35.20, p=0.02) and a non-significant trend for inferior mean DFS. Patients with tumors containing Hras genetic alterations (mutation or polymorphism) had significantly inferior mean OS (p=0.02) compared to those harboring wt Hras and trended towards inferior DFS (p=0.07). Patients had received various treatments such as surgery plus/minus RT and various chemotherapy regimens. A subgroup analysis of 38 patients treated with cetuximab-based regimens showed that wt Hras was associated with higher likelihood of attaining CR or PR to treatment of borderline significance (p=0.06) due to small sample size. Silencing of Hras in Hras-mutant cell lines restored sensitivity to cetuximab and caused a direct downregulation of pERK1/2 levels. Conclusions: Hras genetic alterations are associated with aggressive clinical course and may affect response to cetuximab in HNSCC.