Differential tumor and normal mucosa biomarker modulation by epidermal growth factor receptor (EGFR) inhibition using erlotinib in oral cavity squamous cell carcinoma (OCSCC)
6077 Background: Targeted therapy may improve the therapeutic index in locally advanced head neck cancer if differential EGFR inhibition in tumors compared to the normal mucosa is demonstrated. Based on prior published data, EGFR degradation is an important biomarker of cytotoxicity in a preclinical model. The aim of this pilot study was to determine if there are differences in biomarker modulation between tumor and the normal mucosa and confirm our initial preclinical findings regarding EGFR degradation. Methods: Patients with primary OCSCC requiring surgical resection had normal mucosa and tumor biopsies prior to a test course of erlotinib. Patients received one week of erlotinib 150 mg qd. Repeat tumor and normal mucosal biopsies were obtained at the time of surgical resection to evaluate the effect of the EGFR inhibitor on both tumor and the normal mucosa. Changes in known preclinical markers of EGFR activity (phospho, total EGFR, AKT, STAT3) were measured by immunoblotting assays. In addition, changes in distribution of these biomarkers were analyzed by immunohistochemical analysis. Results: 12 pts were enrolled; 7 pts with paired tumor and normal mucosa biopsies. Tumor specimens showed over-expression of EGFR compared to the normal mucosa (p = 0.005). Erlotinib treatment led to marked inhibition of both pEGFR and EGFR protein (p = 0.004 and p = 0.007, respectively) in tumor biopsies. In contrast, we found heterogeneity in EGFR inhibition in the normal mucosa following erlotinib. (p = 0.1 [pEGFR], and p = 0.07 [EGFR)]) We noted dramatic reduced levels of pSrc and pSTAT3 following erlotinib in tumors compared to untreated matched tumor samples. In addition, levels of p27 were enhanced. Conclusions: Differential EGFR inhibition in tumors compared to the normal mucosa, may suggest that the addition of EGFR inhibitors to chemo-RT or accelerated RT, whose dose limiting toxicity is acute mucositis, may select patients who will benefit from targeted therapy. Our results demonstrate that EGFR inhibition by erlotinib led to marked reduction in EGFR protein levels. EGFR degradation may be an important biomarker in selecting patients predicted to have a response to TKI. These results need further validation. No significant financial relationships to disclose.