Datto, Michael

4086 Background: Abnormalities in the MAPK pathway are potential therapeutic targets in various cancers. However, the clinical impact of alterations in the MAPK pathway in BTC have not been elucidated, especially outside of canonical mutations in KRAS and BRAF. We investigated the clinical outcomes of advanced BTC with MAPK pathway alterations treated with chemotherapy in Japan and the United States. Methods: Patients with advanced BTC who received gemcitabine plus cisplatin as first-line therapy were included from the GOZILA study in Japan and Duke Molecular Registry of Tumors in the US. Genetic abnormalities were detected by Guardant360, a cell-free DNA assay, in Japan and by blood or tissue-based next-generation sequencing (NGS) at Duke University. Two hundred and seven patients with BTC from Japan were included in an exploratory cohort to evaluate the association of MAPK alterations with overall survival (OS) according to MAPK alteration status. One hundred and ten patients with BTC from both Japan and the US harboring oncogenic alterations in the MAPK pathway were included in a biomarker selected cohort to assess the association of specific MAPK alterations with OS. Multivariate analysis was performed using a Cox regression model based on a univariate p-value < 0.2. Results: MAPK pathway-related oncogenic alterations detected in each cohort are shown in the table below. In the exploratory cohort, median OS was shorter for patients with MAPK alterations vs. no MAPK alteration (15.9 m vs. 24.9 m, log-rank p = 0.001). Based on univariate analysis, the following covariates were selected for multivariate analyses: age, prior resection, and MAPK pathway alteration in the exploratory cohort; country, the timing of NGS, distant metastasis, KRAS amplification, and BRAF class 2 mutation in the biomarker selected cohort. In the exploratory cohort, multivariate analysis identified MAPK pathway alterations as an independent predictor of shorter OS with a HR of 1.92 (95% CI = 1.28-2.87, p = 0.001). In the biomarker selected cohort, multivariate analysis identified BRAF class 2 mutations and KRAS amplification as independent predictors of shorter OS with a HR of 16.2 (95% CI = 3.26-80.8, p = 0.001) and 5.97 (95% CI = 1.74-19.3, p = 0.002) respectively. Conclusions: MAPK pathway alterations, especially BRAF class 2 mutation and KRAS amplification, had a significant negative impact on clinical outcomes in BTC receiving first-line chemotherapy. These results are newly confirmed in BTC. [Table: see text]

3571 Background: In colorectal cancer (CRC), mutations in KRAS, NRAS, and BRAF predict resistance to anti-EGFR therapies. In pancreatic ductal adenocarcinoma (PDAC), ~90% of patients harbor KRAS mutations, while KRAS wild-type tumors often have clinically actionable fusion alterations. Thus, in both cancers, the accurate ascertainment of RAS and BRAF driver status is essential. Sequencing of cell-free DNA (cfDNA) from plasma allows convenient assessment of a tumor’s molecular profile, but sensitivity can be limited by low ctDNA shedding. We sought to establish a ctDNA shedding threshold at which actionable driver mutations can be reliably detected. Methods: Molecular reports and matched clinical data were obtained from the Duke Molecular Registry of Tumors and the SCRUM-Japan GOZILA and GI-SCREEN. CRC or PDAC patients with a pathogenic KRAS, NRAS, or BRAF activating point mutation (“driver”) present on tissue next-generation sequencing (NGS) assays and who also had cfDNA assay available were included. Tissue NGS included Foundation One CDx and Oncomine Comprehensive Assay. Guardant 360 (G360) was the sole plasma cfDNA assay. 131 CRC and 24 PDAC cases with 189 total G360 assays met criteria and were included. Samples were analyzed according to detection of the driver mutation and the maximum mutant allele frequency (MAF) of non-driver mutations on G360. An optimal cut-point for max MAF was explored among the CRC and PDAC patients using a maximally selected Wilcoxon rank statistic method. Results: 76.8% of driver mutations were in KRAS, 22.6% in BRAF, and 1.9% in NRAS with an overlap of 1 BRAF and 1 NRAS mutation with a KRAS mutation. Overall sensitivity of G360 for drivers was 83.0% for CRC and 54.2% for PDAC. No variants were detected on G360 in 9.1% of CRC and 37.5% of PDAC. Sensitivity for driver mutations increased with higher maximum non-driver MAF, with MAF > 1% predicting sensitivity > 98% (Table). Optimal cut-point analysis identified MAF of > 0.34% (p < 0.0001), above which the driver was identified in 97% of patients and below which only 27%. Conclusions: In our study, non-driver MAF > 1% on cfDNA NGS predicts high sensitivity for RAS and BRAF mutations and thus is adequate to guide clinical decisions such as anti-EGFR therapy in CRC, evaluation for fusions in PDAC, and validity in clinical trials. MAF ≤0.34% is a clear threshold to consider an assay inadequate and thus seek alternative testing. Sensitivity rises for MAF between 0.35 and 1% but will require greater patient numbers to establish clinically relevant sensitivity thresholds. These results will be updated with additional data for final presentation. [Table: see text]