RAS and BRAF mutations in cell-free DNA are predictive for outcome of cetuximab monotherapy in patients with tissue-tested RAS wild-type advanced colorectal cancer
In metastatic colorectal cancer, RAS and BRAF mutations cause resistance to anti-EGFR therapies, such as cetuximab. Heterogeneity in RAS and BRAF mutations might explain nonresponse in a subset of patients receiving cetuximab. Analyzing mutations in plasma-derived circulating tumor DNA (ctDNA) could provide a more comprehensive overview of the mutational landscape as compared to analyses of primary and/or metastatic tumor tissue. Therefore, this prospective multicenter study followed 34 patients with metastatic colorectal cancer who were tissue-tested as RAS wild-type (exons 2–4) during routine work-up and received third-line cetuximab monotherapy. BRAF mutation status was also tested but did not exclude patients from therapy. At baseline and upon disease progression, cell-free DNA (cfDNA) was isolated for targeted next-generation sequencing (NGS). At 8 weeks, we determined that patients had benefited from treatment. NGS of cfDNA identified three patients with RAS mutations not detected in tumor tissue during routine work-up. Another six patients had a BRAF or rare RAS mutation in ctDNA and/or tumor tissue. Relative to patients without mutations in RAS/BRAF, patients with mutations at baseline had shorter progression-free survival [1.8 versus 4.9 months (P < 0.001)] and overall survival [3.1 versus 9.4 months (P = 0.001)]. In patients with clinical benefit (progressive disease after 8 weeks), ctDNA testing revealed previously undetected mutations in RAS/BRAF (71%) and EGFR (47%), which often emerged polyclonally. Our results indicate that baseline NGS of ctDNA can identify additional RAS mutation carriers, which could improve patient selection for anti-EGFR therapies. Acquired resistance, in patients with initial treatment benefit, is mainly explained by polyclonal emergence of RAS, BRAF, and EGFR mutations in ctDNA.
|Keywords||biomarkers, BRAF, cell-free DNA, cetuximab, colorectal cancer, RAS mutations|
|Persistent URL||dx.doi.org/10.1002/1878-0261.12550, hdl.handle.net/1765/120453|
van Helden, E.J.B., Angus, L., van Oordt, C., Heideman, D.A.M, Boon, E., van Es, S.C., … Verheul, HM. (2019). RAS and BRAF mutations in cell-free DNA are predictive for outcome of cetuximab monotherapy in patients with tissue-tested RAS wild-type advanced colorectal cancer. Molecular Oncology. doi:10.1002/1878-0261.12550