Epidermal Growth Factor Receptor (EGFR) is over-expressed in ~95% of squamous cell carcinomas (SCC). Despite this, therapeutic antibodies targeting EGFR have improved long-term survival in only ~30% of patients treated. Thus, a large fraction of patients treated with anti-EGFR antibodies remain resistant to therapy despite EGFR over-expression. The anti-tumour actions of anti-EGFR monoclonal antibodies involve multiple mechanisms. In particular, anti-EGFR antibodies induce cytotoxicity via immune system-dependent mechanisms such as antibody-dependent cellular cytotoxicity (ADCC). However, the biological determinants of EGFR antibody therapy sensitivity remain unknown. Specifically, it is unknown why a patient, whose tumour over-expresses EGFR, does not respond to therapeutic antibodies directed against EGFR. Since ADCC is dependent upon plasma membrane expression of the target antigen, one could speculate that receptor internalisation rates could impact ADCC. To address this we have developed a novel imaging method which allows us to examine and quantify ligand-induced endocytosis of EGFR in live ex-vivo un-dissociated human SCC. Using confocal microscopy and super-resolution, three dimensional structured illumination microscopy (3D-SIM) we show that 37% of patients do not endocytose over-expressed EGFR in response to ligand stimulation. Using multi-parametric FACS analysis we show that loss of EGFR endocytosis leads to improved ADCC. Finally, we show that reversible small molecule inhibitors of endocytosis can enhance Cetuximab-induced SCC tumour cell death by ADCC and can convert Cetuximab-insensitive SCC cell lines to Cetuximab-sensitive through enhanced ADCC.