EGFR and non-small cell lung carcinoma: In fact, before the third-generation EGFR TKIs developed, a certain amount of small samples clinical studies abroad confirmed that after the failure of advanced NSCLC with gefitinib, erlotinib can achieve a good effect with 5–10% PR and 40–60% SD.[16,17] Why there are different efficacy and cross-resistance spectrum among first-generation EGFR TKIs?