Background: Epidermal growth factor receptor (EGFR) – mutated non-small cell lung cancer (NSCLC) is susceptible to EGFR targeting tyrosine kinase inhibitors (TKI), such as the third generation TKI osimertinib. However, response rate and duration vary between patients. Among others, the specific subtype of EGFR-mutation, its co-occurrence with other genetic alterations, and the detection of phosphorylated EGFR (pEGFR) in the plasma, and its clearance upon treatment were previously identified as markers that predict therapy response. A high proportion of patients with early (3-6 weeks after start) pEGFR clearance from plasma show impressive survival upon single-agent TKI. However, failure to achieve early clearance upon Osimertinib is associated with unfavorable outcome. For these patients, treatment concepts are lacking. Here, we report about the initiation of a clinical trial that evaluates the combination of EGFR-directed TKI and platinum-based chemotherapy as an early treatment escalation strategy for this high-risk patient population. Methods: PACE is a prospective multicenter single-arm investigator-initiated phase II trial. Patients with NSCLC harboring L858R or del19 EGFR mutation, who are treated with first-line Osimertinib are subjected to liquid biopsy-based early response assessment three weeks after start of therapy. Failure to clear pEGFR from plasma at this time point triggers treatment escalation with the addition of platinum-based doublet chemotherapy to the Osimertinib treatment. The primary outcome measure of the trial is progression-free survival (PFS), with the objective to assess the efficacy of biomarker-driven escalation of osimertinib therapy with a combination platinum-based regimen. Secondary outcome measures are the overall response rate (ORR), overall survival (OS), and the Quality of life (QLQ-C30, CTCAE-PROs) of the treated patients. In exploratory analyses, we will assess whether specific patterns of co-mutations are associated with early treatment failure (upon TKI) and pEGFR persistence. Fig. 1 illustrates the trial concept. A sample of 46 subjects achieves 80% power at a 0.05 significance level to detect a PFS of 14.4 months in the experimental treatment group when the PFS of the historic control group is 9.1 months; a total of 400 patients need to be screened within the national Network Genomic Medicine. Enrollment started in 12/2021. The clinical trial is supported by AstraZeneca and Guardant. EudraCT registration number: 2019-004757-88.