EGFR TKIs are standard therapy for advanced NSCLC. In order to define their role in early disease, we implemented a phase II trial of neoadjuvant gefitinib in clinical stage I NSCLC. Tumour shrinkage was seen in 43% of patients, with 11% achieving RECIST partial response (PR). Analysis of molecular markers showed EGFR TKD mutations in 17% of cases, being the only associated with PR. For the first time we defined the histopathological response of NSCLC to these agents, characterized by reduction in tumour cellularity and proliferative index as well as presence of non-mucinous BAC histology. Clinical PR tumours also presented large areas of stromal fibrosis with presence of focal residual tumour. In a characterization of intracellular signalling response, EGFR dephosphorylation in the residues Y1068 and Y1173 was not concordant and only the former was significantly reduced. pAkt Ser473/Akt and Thr308/Akt ratios were significantly reduced but observed among both, clinical responders and resistant patients. Interestingly, reduction in pEGFR Y1068 was significantly associated with increase in tumour cellularity (p=0.047), Ki-67 index (p=0.018) and tumour growth (p=0.019) with a residual perinuclear localization been detected, suggesting a novel mechanism of resistance involving receptor internalization. Finally, we determined that the EGFR protein remains stable up to one hour of post resection ischemia but two to three tumour samples are necessary for an adequate tumour representation. Furthermore, EGFR cytoplasmic compartment presented the best association with clinical response in our cohort. Taking all together, we were able to generate the first clinical trial exploring the use of an EGFR TKI in early NSCLC, characterizing for the first time the histopathological and signalling responses to these agents with an evidence of a potential novel mechanism of resistance. Finally, we observed that multiple samples collection for an adequate tumour representation, and assessment of the cytoplasmic compartment, are warrant.

EGFR TKIs are standard therapy for advanced NSCLC. In order to define their role in early disease, we implemented a phase II trial of neoadjuvant gefitinib in clinical stage I NSCLC. Tumour shrinkage was seen in 43% of patients, with 11% achieving RECIST partial response (PR). Analysis of molecular markers showed EGFR TKD mutations in 17% of cases, being the only associated with PR. For the first time we defined the histopathological response of NSCLC to these agents, characterized by reduction in tumour cellularity and proliferative index as well as presence of non-mucinous BAC histology. Clinical PR tumours also presented large areas of stromal fibrosis with presence of focal residual tumour. In a characterization of intracellular signalling response, EGFR dephosphorylation in the residues Y1068 and Y1173 was not concordant and only the former was significantly reduced. pAkt Ser473/Akt and Thr308/Akt ratios were significantly reduced but observed among both, clinical responders and resistant patients. Interestingly, reduction in pEGFR Y1068 was significantly associated with increase in tumour cellularity (p=0.047), Ki-67 index (p=0.018) and tumour growth (p=0.019) with a residual perinuclear localization been detected, suggesting a novel mechanism of resistance involving receptor internalization. Finally, we determined that the EGFR protein remains stable up to one hour of post resection ischemia but two to three tumour samples are necessary for an adequate tumour representation. Furthermore, EGFR cytoplasmic compartment presented the best association with clinical response in our cohort. Taking all together, we were able to generate the first clinical trial exploring the use of an EGFR TKI in early NSCLC, characterizing for the first time the histopathological and signalling responses to these agents with an evidence of a potential novel mechanism of resistance. Finally, we observed that multiple samples collection for an adequate tumour representation, and assessment of the cytoplasmic compartment, are warrant.