EGFR and lung adenocarcinoma: Somatic activating mutations in the tyrosine kinase domain of the EGFR gene are observed in 15% of patients with lung adenocarcinoma, and more frequently in those with lepidic and acinar subtypes [30,31,32], with exon 19 deletion (62%) and L858R point mutation in exon 21 (38%) being the most common.