EGFR-amplification plus gene expression profiling predicts response to combined radiotherapy with EGFR-inhibition: a preclinical trial in 10 HNSCC-tumour-xenograft models

Background and Purpose: Improvement of the results of radiotherapy by EGFR inhibitors is modest, suggesting significant intertumoral heterogeneity of response. To identify potential biomarkers, a preclinical trial was performed on ten different human squamous cell carcinoma xenografts of the head and neck (HNSCC) studying in vivo and ex vivo the effect of fractionated irradiation and EGFR inhibition. Local tumour control and tumour growth delay were correlated with potential biomarkers, e.g. EGFR gene amplification and radioresponseassociated gene expression profiles.
Material and methods: Local tumour control 120 days after end of irradiation was determined for fractionated radiotherapy alone (30f, 6 weeks) or after simultaneous EGFR-inhibition with cetuximab. The EGFR gene amplification status was determined using FISH. Gene expression analyses were performed using an in-house gene panel.
Results: Six out of 10 investigated tumour models showed a significant increase in local tumour control for the combined treatment of cetuximab and fractionated radiotherapy compared to irradiation alone. For 3 of the 6 responding tumour models, an amplification of the EGFR gene could be demonstrated. Gene expression profiling of untreated tumours revealed significant differences between amplified and non-amplified tumours as well as between responder and non-responder tumours to combined radiotherapy and cetuximab.
Conclusion: The EGFR amplification status, in combination with gene expression profiling, may serve as a predictive biomarker for personalized interventional strategies regarding combined treatment of cetuximab and fractionated radiotherapy and should, as a next step, be clinically validated.