P2.03-33 ctDNA Levels Significantly Predicts Survival in NSCLC Patients with an EGFR Activating Mutation

Abstract

Circulating tumor DNA (ctDNA) have been shown to be useful for non-invasive biomarker testing in non-small cell lung cancer (NSCLC). In addition, there is growing evidence supporting that ctDNA levels can be useful for tumor response to treatment monitoring. Nevertheless, data from large prospective clinical longitudinal studies still limited. 300 plasma samples from 100 advanced NSCLC patients, with tumors harboring an EGFR activating mutation and treated with a first line tyrosine Kinase inhibitor were analyzed. Samples were collected before the start of treatment, at first follow up evaluation, at 7 month and at disease progression. ctDNA was analyzed by dPCR. Median follow up was 11.3 months. There were not significant differences in progression free survival (PFS) or overall survival (OS) according to treatment (erlotinib, afatinib or gefitinib). Patients harboring a deletion in exon 19 or a mutation in exon 21 exhibited better survival than those with an insertion in exon 20 (P<0.001). dPCR detected EGFR sensitizing mutation in 77% of the pre-treatment samples. ctDNA levels before the start of the treatment did not significantly predict survival, although a tendency was observed, with patients with high levels of ctDNA showing poorer outcome. On the contrary, patients in which the EGFR sensitizing mutation was undetectable at first follow up had a markedly better PFS and OS (HR=2.7; 95IC= 1.4-5.5 and HR= 5.5 95IC: 1.8-17 respectively). In the same way, patients in which the EGFR sensitizing mutation remained negative at 7months had a significantly increased PFS (HR: 2.8; 95IC: 1.2-6.6). None of the patients with undetectable levels at 7 months has deceased. ctDNA levels is of prognostic significance in EGFR positive NSCLC patients with advance disease and can be useful to monitor treatment outcome