EGFR and neoplasm: In addition, the combination of osimertinib with the MEK inhibitor selumetinib was found to prevent EGFR-TKI resistance both in vitro and in vivo.62 Ortiz-Cuaran et al.54 identified a KRAS G12S mutation on tumour re-biopsy at the onset of acquired resistance to second-line osimertinib.