Supplementary Material for: FGFR4 Is a Potential Predictive Biomarker in Oral and Oropharyngeal Squamous Cell Carcinoma

Objective: The aim of this study was to investigate whether fibroblast growth factor receptor 4 (FGFR4) could serve as a potential therapeutic target, prognostic biomarker or biomarker predicting radiotherapy sensitivity in oral squamous cell carcinoma (OSCC) and oropharyngeal squamous cell carcinoma (OPSCC). Methods: FGFR4 immunohistochemistry and FGFR4/CEN5q FISH were performed on tissue microarrays from 212 OSCC and 238 OPSCC patients. FGFR4 genotypes were determined by PCR and DNA sequencing in 76 random OPSCC samples. The response to radiotherapy was evaluated 3 months after the last radiotherapy treatment session by a head and neck radiation oncologist and/or surgeon during clinic visits. The results were correlated to overall survival and response to radiotherapy. Results: The FGFR4 protein was overexpressed in 64% (153/238) of OPSCCs and 41% (87/212) of OSCCs. The FGFR4 gene was amplified in 0.47% (1/212) of OSCCs and 0.42% (1/238) of OPSCCs, and the FGFR4 Gly388Arg polymorphism was detected in 62% (47/76) of OPSCCs. FGFR4 protein expression, FGFR4 gene copy numbers and FGFR4 genotypes were not related to overall survival or response to radiotherapy in OSCC or OPSCC. Conclusion: FGFR4 is frequently overexpressed in OSCC and OPSCC in the absence of gene amplification, and may serve as a potential predictive marker for FGFR4-directed targeted therapy in OSCC and OPSCC.