Baseline Plasma EGFR Circulating Tumour DNA Levels in a Pilot Cohort of EGFR-Mutant Limited-Stage Lung Adenocarcinoma Patients Undergoing Radical Lung Radiotherapy.

The use of circulating cell-free tumour DNA (ctDNA) is established in metastatic lung adenocarcinoma to detect and monitor sensitising EGFR mutations. In early-stage disease, there is very little data supporting its role as a potential biomarker. We report on a prospective cohort of 9 limited-stage EGFR mutant lung cancer patients who were treated with radical radiotherapy. We looked at baseline plasma EGFR ctDNA and noted the detection rates to be higher in locally advanced disease. At a median follow-up of 13.5 months, an association between a detectable pre-radiotherapy plasma EGFR ctDNA and early tumour relapse (155 days vs. NR, p = 0.004) was noted. One patient with persistent plasma EGFR ctDNA predated radiological progression. The role of ctDNA in early-stage lung cancer is developing. Plasma EGFR ctDNA could be a useful biomarker in lung cancer patients undergoing radical treatments for staging, prognostication, and follow-up. These preliminary findings should be explored in larger studies.