EGFR and neoplasm: In addition to detection of the onset of a secondary EGFR mutation (namely the C797S mutation, less frequent than the EGFR T790M mutation) as an indication of a new mechanism of osimertinib resistance, other genomic alterations occurring in different genes—notably in MET, KRAS, BRAF, or RET—can also be detected in cf-DNA in osimertinib-treated patients at tumour progression [195,202,203,204].