Abstract 30: Quantitative monitoring of EGFR mutations in urinary circulating tumor DNA enables non-invasive pharmacodynamic assessment of anti-EGFR drug response

Background: Acquisition of the EGFR T790M resistance mutation is a hallmark of disease progression in patients with metastatic EGFR mutant lung adenocarcinoma treated with first generation anti-EGFR inhibitors. Utilizing a single copy sensitivity mutation detection platform and implementing daily collection of urine samples, we sought to demonstrate the feasibility of detecting EGFR mutations in urinary ctDNA and understand mechanisms of resistance to targeted therapies in patients with EGFR-mutated lung adenocarcinoma. Methods: In a biomarker study of 100 patients with EGFR-mutant metastatic lung adenocarcinoma (34 patients enrolled), urine was collected at either daily or monthly time points up to 4 months prior to radiologic detection of progression on erlotinib, and at multiple time points post-progression on next line therapy. Urinary ctDNA was extracted by a method that preferentially isolates short, fragmented ctDNA. Quantitative analysis of EGFR activating mutations and T790M resistance mutation was performed using blocker technology and PCR enrichment coupled with NGS detection (MiSeq). Urine was collected daily after the initiation of second line anti-EGFR therapy in 10 patients. Early pharmacodynamic events that occur within the first hours to days of anti-EGFR therapy were further studied by quantitating ctDNA for EGFR exon 19deletions, L858R, and T790M. Results: Interim analysis was conducted on 34 patients receiving first line anti-EGFR therapy with erlotinib; twenty-two of 34 patients demonstrated radiographic progression. Analysis of longitudinal samples revealed that the EGFR T790M mutation was detected in the urine specimens of 15 out of 22 (68%) patients on erlotinib. All 10 patients who were positive for T790M mutation by tissue were also positive by urine. Urine testing identified five additional T790M-positive patients who had a high clinical suspicion of T790M progressive disease. Three of these patients were tissue negative but both plasma and urine positive for T790M. EGFR T790M was detected up to 15 weeks prior to radiolographic detection of progression on first line erlotinib. Early peaks in ctDNA on days 1-4 correlated with tumor lysis. An observed sustained decrease in mutational levels after week 1 of therapy confirms the cytostatic effect of the tyrosine kinase inhibitor (TKI). The size of the initial peaks in ctDNA for EGFR exon 19deletions, L858R, and T790M correlated with CT radiographic response after two cycles of therapy. Conclusion: We demonstrate that the T790M mutation can be successfully detected in urinary ctDNA months before progression on anti-EGFR TKIs. Urinary ctDNA testing identifies additional patients who potentially are eligible for anti-T790M treatment. Initial results from 10 patients demonstrated that kinetic changes in EGFR ctDNA mutational load after drug adminstration can be used with pharmacokinetic data to better understand dyanmic changes in tumor biology, drug bioavailability, and assist in early drug development. The clinical utility of daily kinetic monitoring of ctDNA in urine after drug adminstration is being further validated in a larger study. Citation Format: Hatim Husain, Karena Kosco, Saege Hancock, Errin Samuelsz, Shiloh Guerrero, Brian Woodward, Cecile Rose Vibat, Vlada Melnikova, Mark Erlander, Scott Lippman, Razelle Kurzrock. Quantitative monitoring of EGFR mutations in urinary circulating tumor DNA enables non-invasive pharmacodynamic assessment of anti-EGFR drug response. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Integrating Clinical Genomics and Cancer Therapy; Jun 13-16, 2015; Salt Lake City, UT. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(1_Suppl):Abstract nr 30.