Abstract 3977: Clinical validation of cell-free circulating tumor DNA to detect therapy resistance and disease progression in metastatic colorectal cancer patients

Abstract

Abstract Introduction: DNA mutation analysis in individual patients paves the road towards personalized medicine, in which prognosis and therapy prediction are determined based on gene mutations. For example, it is known that RAS mutations are a negative predictor biomarker for response to therapeutic monoclonal antibodies directed against the epithelial growth factor receptor (EGFR) in metastasized colorectal cancer (mCRC) patients. Anti-EGFR treatment is expensive and 80-90% of the patients who do not benefit from anti-EGFR therapy suffer from the negative side-effects. Therefore, better prediction and monitoring of anti-EGFR treatment response is necessary. Cell-free circulating tumor DNA (ctDNA) derived from blood plasma is expected to improve stratification by early detection of therapy resistance and disease progression. Aim: The general aim of this study is to advance towards clinical implementation of ctDNA-based tests as molecular biomarkers to improve disease management of mCRC patients. In particular, we investigate the added value of liquid biopsy mutation analysis for (1) assessment of primary and acquired resistance to anti-EGFR treatment using a gene panel, compared to the conventional tissue analyses, and (2) for detection of disease progression, compared to conventional computed tomography (CT) imaging. Methods: CAIRO5 is a multicenter, randomized, phase 3 clinical trial of the Dutch Colorectal Cancer Group and includes patients with initially unresectable, liver-only mCRC, as confirmed by a central panel of liver surgeons/radiologists. Liquid biopsies are longitudinally collected in cell-save Streck tubes at baseline and during follow-up, in parallel with the CT imaging (every 2 to 3 months). In ctDNA, RAS/RAF hotspot mutations are analyzed by droplet digital PCR (ddPCR), while a panel of 33 genes will be analyzed using ultrasensitive next generation sequencing approaches. Results: The nation-wide multicenter logistics for longitudinal blood sample collection and plasma processing has been established, with participation of more than 55 Dutch hospitals. At present (November 2018), over 350 patients have been included from whom more than 850 blood samples were obtained. Based on tissue analyses, 59% of these patients harbors a RAS/RAF mutation (48% KRAS, 5% NRAS, 6% BRAF). Concordance between tissue biopsy and liquid biopsy was determined in a subset of patients and showed a >90% concordance for KRAS at codons 12, 13 or 61. In addition, radiologic evaluations of the CT images are collected and the lead time for recurrence will be compared with ctDNA analysis. Results of a first selection of patients will be presented. Conclusion: The liquid biopsy ctDNA and clinical data obtained in this study will provide the input for a health technology assessment yielding recommendations for clinical implementation of ctDNA applications. Citation Format: Iris van 't Erve, Alessandro Leal, Karen Bolhuis, Jillian Phallen, Nicole van Grieken, Veerle Coupé, Annegien Broeks, Daan van den Broek, Victor Velculescu, Cornelis Punt, Gerrit Meijer, Remond Fijneman. Clinical validation of cell-free circulating tumor DNA to detect therapy resistance and disease progression in metastatic colorectal cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3977.