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Rechallenge with epidermal growth factor (EGFR) inhibitors represents a promising therapeutic strategy in patients with refractory RAS/BRAF wild-type metastatic colorectal cancer (mCRC). The maximal benefit is observed in patients without resistance mutation at the baseline plasma circulating tumor DNA (ctDNA) evaluation. In the CAVE and VELO clinical trials, 1 out of 4 patients had ctDNA RAS/BRAF mutant disease at pretreatment liquid biopsy assessment. There was no direct association between the length of anti-EGFR drug-free interval and the presence of plasma ctDNA RAS/BRAF mutations at pretreatment liquid biopsy analysis. Interestingly, even the disappearance of mutant clones was time-dependent, and resistance mutations were found at liquid biopsy analysis in approximately 15% of patients after 18 or more months of anti-EGFR drug-free window. These results support the use of liquid biopsy to appropriately select amenable patients to EGFR inhibitor rechallenge. Rechallenge with anti-EGFR drugs represents a promising strategy in refractory RAS/BRAF wild-type (WT) metastatic colorectal cancer (mCRC). We performed the pooled analysis of the CAVE and VELO studies to evaluate the percentage of patients with WT circulating tumor DNA (ctDNA) tumors and the association of mutational status with time from the last anti-EGFR drug administration. At baseline, 97/129 patients had RAS/BRAF WT plasma ctDNA, while 32/129 had RAS/BRAF mutated plasma ctDNA. Median anti-EGFR drug-free interval was 10.6 (CI 95%, 8.9-13.4) months in the plasma RAS/BRAF mutant group as compared to 13.0 (CI 95%, 11.1-16.6) months in RAS/BRAF WT group (p = 0.169). To investigate the time window of the RAS/BRAF mutant cancer cell clone disappearance, descriptive analysis using different time points was performed. No difference in the proportion of patients whose baseline plasma ctDNA was RAS/BRAF WT or mutated was found between 4 and 18 months since the last administration of anti-EGFR drugs. In contrast, 38/44 of patients with anti-EGFR drug-free interval of 18 months or more displayed a ctDNA RAS/BRAF WT status. Taken together, these results shows that the length of anti-EGFR free interval is not a sufficient criterion for patient selection, supporting the role of liquid biopsies for improving treatment efficacy.

Current therapies for chemo-refractory metastatic colorectal cancer (mCRC) have limited efficacy. Rechallenge with epidermal growth factor receptor (EGFR) inhibitors in RAS wild-type (WT) mCRC could be valuable in this setting. In VELO, a randomized two-arm phase 2 trial, anti-EGFR monoclonal antibody panitumumab plus standard-of-care trifluridine/tipiracil (31 patients, arm B) was compared to trifluridine/tipiracil (31 patients, arm A) as third-line therapy (ClinicalTrials.gov Identifier NCT05468892). Primary endpoint, progression-free survival (PFS), was met. Median PFS was 4.0 months in arm B versus 2.5 months in arm A [hazard ratio (HR): 0.48; 95% CI 0.28–0.82; P = 0.007]. Baseline plasma RAS/BRAF WT circulating tumor DNA identified patients obtaining prolonged clinical benefit with panitumumab plus trifluridine/tipiracil as compared to trifluridine/tipiracil with PFS rates at 6 months of 38.5% versus 13% and at 12 months of 15.4% versus 0%, respectively. These findings warrant further development for liquid biopsy-guided anti-EGFR rechallenge combination strategies in chemo-refractory RAS WT mCRC.

IMPORTANCE: Rechallenge therapy with anti–epidermal growth factor receptor (EGFR) drugs has been suggested in patients with chemo-refractory RAS wild-type (WT) metastatic colorectal cancer (mCRC) after initial response to anti–EGFR-based first-line treatment. The association of treatment with cetuximab plus avelumab with overall survival (OS) may be worthy of investigation in this setting. OBJECTIVE: To assess the efficacy and safety of cetuximab rechallenge therapy plus avelumab. DESIGN, SETTING, AND PARTICIPANTS: This single-arm, multicenter phase 2 trial enrolled patients from August 2018 to February 2020. Eligible patients with RAS WT mCRC had a complete or partial response to first-line chemotherapy plus anti-EGFR drugs, developed acquired resistance, and failed second-line therapy. Baseline circulating tumor DNA (ctDNA) for KRAS, NRAS, BRAF, and EGFR-S492R mutation analysis was done. INTERVENTIONS: Patients received avelumab (10 mg/kg every 2 weeks) and cetuximab (400 mg/m(2) and, subsequently, 250 mg/m(2) weekly) until disease progression or unacceptable toxic effects. MAIN OUTCOMES AND MEASURES: The primary end point was OS. Secondary end points were progression-free survival (PFS), overall response rate (ORR), and safety. RESULTS: Seventy-seven patients were enrolled (42 men, 35 women; median age, 63 years); 71 had microsatellite stable tumors (MSS), 3 microsatellite instability-high tumors (MSI-H), 3 unknown. The study met the primary end point, with median OS (mOS) of 11.6 months (95% CI, 8.4-14.8 months). Median PFS (mPFS) was 3.6 months (95% CI, 3.2-4.1 months). Common grade-3 adverse events were cutaneous eruption, 11 (14%), and diarrhea, 3 (4%). For 67 of 77 (87%) patients, baseline analysis of plasma circulating tumor DNA (ctDNA) for KRAS, NRAS, BRAF, and EGFR-S492R variations was feasible. Forty-eight patients had WT disease, whereas 19 had mutations. Patients with RAS/BRAF WT ctDNA had mOS of 17.3 months (95% CI, 12.5-22.0 months) compared with 10.4 months (95% CI, 7.2-13.6 months) in patients with mutated ctDNA (hazard ratio [HR], 0.49; 95% CI, 0.27-0.90; P = .02). The mPFS was 4.1 months (95% CI, 2.9-5.2 months) in RAS/BRAF WT patients compared with 3.0 months (95% CI, 2.6-3.5 months) in patients with mutated ctDNA (HR, 0.42; 95% CI, 0.23-0.75; P = .004). CONCLUSIONS AND RELEVANCE: The findings of this single-arm phase 2 trial suggest that cetuximab plus avelumab is an active, well tolerated rechallenge therapy in RAS WT mCRC. Plasma ctDNA analysis before treatment may allow selection of patients who could benefit. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT04561336

Tumor heterogeneity represents a possible cause of error in detecting predictive genetic alterations on tumor tissue and can be overcome by testing alterations in circulating tumor DNA (ctDNA) using liquid biopsy. We assessed 72 consecutive patients with a diagnosis of metastatic colorectal cancer (mCRC) using Idylla&trade, Biocartis, a fully automated platform that evaluates the most frequent mutations of KRAS, NRAS and BRAF genes. We correlated the results of liquid biopsy and standard tissue-based next generation sequencing (NGS) analyses to patient clinical features. The overall agreement was 81.94%. Concordance was 85.71% and 96.15% in treatment-na&iuml, ve patients and in the patient subgroup with liver metastases, respectively. In liver metastases positive, treatment-na&iuml, ve patients, sensitivity, specificity and positive predictive value (PPV) were 92.31%, 100% and 100%, respectively. Circulating mutational fraction (CMF) was significantly higher in patients with liver metastases and high carcinoembryonic antigen (CEA) levels. In a subgroup of patients pre-treated with anti-Epidermal Growth Factor Receptor (EGFR) agents, emerging KRAS mutations were evidenced in 33% of cases. Testing RAS/BRAF mutations on plasma using the Idylla&trade, Biocartis platform is feasible and reliable in mCRC patients in clinical practice.

3578 Background: Promising antitumor activity of so called rechallenge treatment with anti-epidermal growth factor receptor (EGFR) drugs in patients with RAS wild type (RAS WT) metastatic colorectal cancer (mCRC) has been recently reported. Beside the absence of resistance mutations at plasma circulating tumor DNA (ctDNA) analysis, no biomarkers of response to anti-EGFR rechallenge strategy have been identified. Methods: We conducted the single arm phase II CAVE mCRC trial to evaluate the combination of cetuximab as rechallenge plus avelumab treatment in 77 RAS WT mCRC patients, with complete (CR) or partial response (PR) to first line chemotherapy plus anti-EGFR drugs, who developed acquired resistance and received a subsequent line of therapy. A post-hoc baseline analysis of circulating tumor DNA (ctDNA) for KRAS, NRAS, BRAF and EGFR-S492R mutations was performed for 67/77 (87%) patients. The correlation of skin toxicity (ST) and other clinical variables with OS, PFS and response rate (RR) was assessed. Results: Cetuximab plus avelumab provided in the intention to treat population (ITT) median overall survival (mOS) of 11.6 months [95% Confidence Interval (CI), 8.4-14.8] and median PFS (mPFS) of 3.6 months (95% CI, 3.2-4.1) with a manageable toxicity profile. Thirty-three (42.9%) patients experienced grade 2-3 ST with mOS of 17.8 months (CI 95% 14.9-20.7), whereas 44 (57.1%) patients with grade 0-1 ST exhibited mOS of 8.2 months (CI 95% 5.6-11), (HR 0.51, CI 95% 0.29-0.89, P = 0.019). mPFS was 4.6 months (CI 95% 3.5-5.8) in patients with grade 2-3 ST, compared to 3.4 months (CI 95% 2.8-4.1) in patients with grade 0-1 ST (HR 0.49, CI 95% 0.3-0.8, P = 0.004). Grade 2-3 ST and baseline RAS/BRAF/EGFR WT ctDNA were the only variables with statistically significant effect on OS both at univariate and multivariate analyses. ST, number of metastatic sites ≤2, surgery of primary tumor and RAS/BRAF/EGFR WT ctDNA were associated with an improvement in PFS only at univariate analysis. In the 33 patients with grade 2-3 ST, 1 (3%) CR, 2 (6.1%) PR and 24 (72.7%) stable disease (SD) were observed, with disease control rate (DCR) of 81.8%. In the 44 patients with grade 0-1 ST 0 CR, 3 (6.8%) PR, 20 (45.5%) SD, with 52.3% DCR were reported. Conclusions: Cetuximab plus avelumab is effective and well tolerated as rechallenge treatment in mCRC. ST is a clinical biomarker for the identification of RAS/BRAF mCRC patients that could benefit from anti-EGFR rechallenge. Clinical trial information: NCT04561336.