P1.09-21 Circulating Tumor DNA Improves Genotypification and Detection of Targetable Alterations in Selected Lung Cancer Patients

Abstract

Several studies have shown that NSCLC genomic background among Hispanics differs from other populations. The finding of low frequency genomic alterations in cfDNA to increase diagnostic accuracy in NSCLC could refine the treatment. We hypothesized that cfDNA can be an alternative or complement for detection of low frequency genomic targets. We aimed to understand the landscape of cfDNA-identified genomic drivers in a cohort of patients (pts) with NSCLC of Hispanic ancestry. We collected data from 51 Hispanic pts (Mexico and Colombia) with advanced NSCLC (Stage III/IV) who previously underwent tissue screening for ALK, EGFR, and ROS1. CfDNA was extracted from plasma and analyzed by a commercial NGS test (Guardant360â) which detects genomic alterations (alts) in up to 73 genes. Median age was 56 years (31-83). Most pts were female (64.7%) and never smokers (76.5%). 94% of cases (48/51) had cfDNA detectable alts with a mean number of 3.37 cfDNA alts per test (range, 1 -10). Of the 48 pts with cfDNA genomic alts, 23 (47.9%) had a known genomic driver (EGFR (27.4%), TP53 (13.7%), ALK (7.8%), KRAS (5.8%), and BRAF (3.9%)). Interestingly, cfDNA was able to detect some genomic alts previously undetected by tissue biopsy (either due to false negatives or to technical limitations such as insufficient or low-quality DNA). In the case of EGFR, 12 pts had EGFR alts through cfDNA which were previously undetected by tissue biopsy. Similarly, cfDNA detected 3 alterations in ALK which were previously undetected by tissue sample. Of 48 pts, 35.4% were switched to a targeted therapy as a result of alts detected through cfDNA, with adequate responses: disease control rate was 82.4% (partial response 47.2% and stable disease 35.2%) and progression free survival was 7.4 months (95%CI 2.6-28.1). In a selected population of young Hispanics (especially never smokers and women) with NSCLC the use of comprehensive cfDNA analysis allowed a treatment change in 35% of the cases. Our data confirms the usefulness of Guardant360â as non-invasive panel to identify genomic alts in cfDNA.