What is the importance of finding EGFR sensitizing mutations such as exon 19 or exon 21 in NSCLC? What is their relationship to sensitivity to TKIs, such as erlotinib, gefitinib, and afatinib?

What is the importance of finding EGFR sensitizing mutations such as exon 19 or exon 21 in NSCLC? What is their relationship to sensitivity to TKIs, such as erlotinib, gefitinib, and afatinib?

What is the importance of finding EGFR sensitizing mutations such as exon 19 or exon 21 in NSCLC? What is their relationship to sensitivity to TKIs, such as erlotinib, gefitinib, and afatinib?