Abstract C100: KRAS mutations in circulating cell-free DNA of colorectal cancer patients in progression after MoAb anti-EGFR therapy.

Abstract

Abstract Background: Anti-EGFR therapy is a standard treatment strategy in patients with metastatic colorectal cancer (mCRC) with a wild type KRAS status. Inevitably, resistance mechanisms arise in the majority of patients during treatment, and re-biopsy of the tumor is the only way to characterize the molecular alterations responsible for the resistance. Circulating cell-free tumor DNA (cftDNA) is released into the bloodstream by tumor cells, and its recovery could represent a valid non-invasive alternative to biopsy for the molecular characterization of the tumor. The aim of this study is to search for KRAS mutations in the cftDNA of mCRC patients in progression after treatment with an anti-EGFR MoAb. Methods: Fourteen mCRC patients with KRAS wild type status identified previously in tumor tissue by pyrosequencing were treated with an anti-EGFR MoAb until progression. cftDNA was extracted from 1-2 ml of plasma collected at baseline and after progression. Digital Real Time PCR was performed for KRAS G12D and G12V mutations using a QX100™ ddPCR™ System (Bio-Rad). Samples were then loaded into a droplet reader that discriminates between the different fluorescence amplitudes on the basis of target gene amplification. Results: KRAS mutation analysis performed by Digital PCR revealed that mutations (2 G12V and 1 G12D) were present in cftDNA extracted after progression in 3 (21%) of the 14 patients. KRAS analysis was then also performed in DNA extracted from primary tumor tissue and from basal cftDNA. Interestingly, the same mutations were found in the corresponding tumor tissue, confirming the higher sensitivity of Digital PCR with respect to pyrosequencing analysis. Moreover, in 2 of the 3 patients, the KRAS mutation was also present in basal cftDNA. Discussion: Our preliminary results reveal that cftDNA could be a suitable non-invasive approach for the molecular characterization of tumors and could be especially useful to monitor the development of resistance mechanisms, thus avoiding the need for re-biopsy. We also showed that KRAS mutations would not seem to represent a mechanism of acquired resistance to anti-EGFR MoAbs in mCRC patients and are probably present in minor clones at baseline but not detected by standard methods. The use of highly sensitive methods, such as Digital PCR, could enable us to detect these minor mutations in tumor tissue and to monitor response to anti-EGFR MoAbs using cftDNA. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C100. Citation Format: Paola Ulivi, Marzia Del Re, Alessandro Passardi, Giorgia Marisi, Dino Amadori, Fabio Casacci, Martina Valgiusti, Wainer Zoli, Romano Danesi. KRAS mutations in circulating cell-free DNA of colorectal cancer patients in progression after MoAb anti-EGFR therapy. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C100.