In the case of Non-Small Cell Lung Cancer (NSCLC), the presence of the Epithelial Growth Factor Receptor (EGFR) T790M mutation in ctDNA may be detectable months before radiological progression and can be used to switch from EGFR tyrosine kinase inhibitors (TKIs) to osimertinib [117]. The gene discussed is EGFR; the disease is non-small cell lung carcinoma.