Clinical Validation of Plasma-Based Genotyping for RAS and BRAF V600E Mutation in Metastatic Colorectal Cancer: SCRUM-Japan GOZILA Substudy.

PURPOSE: Circulating tumor DNA (ctDNA) genotyping on the basis of next-generation sequencing (NGS) may guide targeted therapy for metastatic colorectal cancer (mCRC). However, the validity of NGS-based ctDNA genotyping for RAS/BRAF V600E mutation assessment and the efficacy of anti-EGFR and BRAF-targeted therapies on the basis of ctDNA results remains unclear. PATIENTS AND METHODS: The performance of NGS-based ctDNA genotyping for RAS/BRAF V600E mutation assessment was compared with that of a validated polymerase chain reaction-based tissue testing in patients with mCRC enrolled in the GOZILA study, a nationwide plasma genotyping study. The primary end points were concordance rate, sensitivity, and specificity. The efficacy of anti-EGFR and BRAF-targeted therapies on the basis of ctDNA were also evaluated. RESULTS: In 212 eligible patients, the concordance rate, sensitivity, and specificity were 92.9% (95% CI, 88.6 to 96.0), 88.7% (95% CI, 81.1 to 94.0), and 97.2% (95% CI, 92.0 to 99.4) for RAS and 96.2% (95% CI, 92.7 to 98.4), 88.0% (95% CI, 68.8 to 97.5), and 97.3% (95% CI, 93.9 to 99.1) for BRAF V600E, respectively. In patients with a ctDNA fraction of ≥1.0%, sensitivity rose to 97.5% (95% CI, 91.2 to 99.7) and 100% (95% CI, 80.5 to 100.0) for RAS and BRAF V600E mutations, respectively. In addition to a low ctDNA fraction, previous chemotherapy, lung and peritoneal metastases, and interval between dates of tissue and blood collection were associated with discordance. The progression-free survival of anti-EGFR therapy and BRAF-targeted treatment was 12.9 months (95% CI, 8.1 to 18.5) and 3.7 (95% CI, 1.3 to not evaluated) months, respectively, for matched patients with RAS/BRAF V600E results by ctDNA. CONCLUSION: ctDNA genotyping effectively detected RAS/BRAF mutations, especially with sufficient ctDNA shedding. Clinical outcomes support ctDNA genotyping for determining the use of anti-EGFR and BRAF-targeted therapies in patients with mCRC.

Clinical Validity of Plasma-Based Genotyping for Microsatellite Instability Assessment in Advanced GI Cancers: SCRUM-Japan GOZILA Substudy.

PURPOSE: Circulating tumor DNA (ctDNA) genotyping may guide targeted therapy for patients with advanced GI cancers. However, no studies have validated ctDNA genotyping for microsatellite instability (MSI) assessment in comparison with a tissue-based standard. PATIENTS AND METHODS: The performance of plasma-based MSI assessment using Guardant360, a next-generation sequencing-based ctDNA assay, was compared with that of tissue-based MSI assessment using a validated polymerase chain reaction-based method in patients with advanced GI cancers enrolled in GOZILA study, a nationwide ctDNA profiling study. The primary end points were overall percent agreement, positive percent agreement (PPA), and negative percent agreement. The efficacy of immune checkpoint inhibitor therapy was also evaluated. RESULTS: In 658 patients with advanced GI cancers who underwent both plasma and tissue testing for MSI, the overall percent agreement, PPA, and negative percent agreement were 98.2% (95% CI, 96.8 to 99.1), 71.4% (95% CI, 47.8 to 88.7), and 99.1% (95% CI, 98.0 to 99.7), respectively. In patients whose plasma samples had a ctDNA fraction ≥ 1.0%, the PPA was 100.0% (15/15; 95% CI, 78.2 to 100.0). Three patients with MSI-high (MSI-H) tumors detected only by ctDNA genotyping achieved clinical benefits after receiving anti-programmed cell death 1 therapy with the progression-free survival ranging from 4.3 to 16.7 months. One patient with an aggressive cancer of an unknown primary site benefited from pembrolizumab after rapid detection of MSI-H by ctDNA genotyping. CONCLUSION: ctDNA genotyping was able to detect MSI with high concordance to validated tissue-based MSI testing, especially in patients with tumors that have sufficient ctDNA shedding. Furthermore, ctDNA genotyping enabled identification of patients with MSI-H tumors who benefited from immune checkpoint inhibitor treatment.