Abstract PR009: Application of Liquid Biopsy-RECIST (LB-RECIST) criteria to track metastatic colorectal cancer (mCRC) molecular response in first-line (1L) setting: Findings from the PLATFORM-B study
Authors: Martelli Valentino , Vidal Joana , Fernández-Rodríguez Maria Concepción , García-Alfonso Pilar , Páez David , Gibert Joan , Linares Jennifer , Sibilio Annarita , Alonso Vicente , Cano Maria Teresa , Santos Cristina , Duran Gema , Élez Elena , Manzano José Luis , Garcia-Carbonero Rocio , Ferreiro Reyes , Losa Ferran , Pineda Estela , Sastre Javier , Gomez-España Auxiliadora , Toledo Rodrigo , Rivera Fernando , Bellosillo Beatriz , Tabernero Josep , Salazar Ramon Ramon , Aranda Enrique , Montagut Clara 
Published: November 2024

Introduction: Circulating tumor DNA (ctDNA) analysis is a minimally invasive and reproducible method to explore tumor molecular biology. Recently, Gouda et al. proposed the LB-RECIST criteria to monitor molecular response, validating them on a heterogeneous metastatic population. However, data on mCRC are lacking. Here, we report the first attempt to apply LB-RECIST in the multicenter prospective PLATFORM-B study, which enrolled 130 mCRC patients (pts) receiving 1L standard therapy, with ctDNA analysis performed at different time points. Materials and Methods: Baseline (BL) and week 8 (W8) plasma samples were analyzed using a targeted NGS-based approach (Ion S5 system). Changes in ctDNA detectability were assessed to determine molecular response as per qualitative LB-RECIST criteria: Group1 (G1, detectable ctDNA at BL and W8); Group2 (G2, detectable BL and undetectable W8); Group3 (G3, undetectable BL and detectable W8); Group4 (G4, undetectable at BL and W8). Changes in aggregate variant allele frequency (VAF) - the sum of all VAFs of the studied genes in a sample - were used to assess quantitative LB-RECIST responses: ctDNA Complete Response (CCR, clearance after initial detectability), Partial Response (CPR, decrease &gt;10%), Stable Disease (CSD, no change or decrease &lt;10%), Progressive Disease (CPD, increase &gt;10% or new mutations), and Non-measurable Disease (CND, undetectable at BL and W8). Molecular results were correlated with clinical outcomes. Statistically significant differences were assessed across different groups using 2-sided P values with an α ≤ .05 level of significance. Results: Overall, 79 pts had paired BL and W8 samples. Quantitative LB-RECIST identified 32 CCR, 18 CND, 20 CPR, 8 CPD, and 1 CSD cases. Qualitative LB-RECIST found 22 G1, 32 G2, 7 G3, and 18 G4 cases. Radiological RECIST identified 6 CR, 47 PR, 21 SD, and 5 PD. CCR showed the highest survival rates: with a median follow-up of 25 months (mo) (range: 1–49), median progression-free survival (mPFS) was not reached (NR) and median overall survival (mOS) was 41.8 mo. The CND group had similar rates (mPFS NR; mOS 41.1 mo). CPR and CPD had the poorest outcomes: for CPR, mPFS was 12.7 and mOS 16.4 mo; for CPD, mPFS and mOS were 11.9 and 25.5 mo, respectively. In the G1, G2, G3, and G4 groups, mPFS was 11.9, NR, 14.2, and NR, respectively, while mOS was 16.4, 41.8, 33.4, and 41.1 mo. Kaplan-Meier analysis of the quantitative groups showed statistically significant differences (P &lt; .0001) for both PFS and OS curves. The same level of significance was found in the qualitative groups. Conclusion: LB- RECIST can be a rapid and reproducible method to assess molecular response in mCRC. However, concerns remain. The CND group (23% of cases) showed survival rates similar to the CCR group, as observed also between G4 and G2. These data suggest that absence of ctDNA at W8 is the best surrogate for OS. Moreover, CPD had higher OS rates than CPR, but similar PFS. Further investigations in larger populations are needed to refine these criteria and improve molecular response stratification

Citation Format: Valentino Martelli, Joana Vidal, Maria Concepción Fernández-Rodríguez, Pilar García-Alfonso, David Páez, Joan Gibert, Jennifer Linares, Annarita Sibilio, Vicente Alonso, Maria Teresa Cano, Cristina Santos, Gema Duran, Elena Élez, José Luis Manzano, Rocio Garcia-Carbonero, Reyes Ferreiro, Ferran Losa, Estela Pineda, Javier Sastre, Auxiliadora Gomez-España, Rodrigo Toledo, Fernando Rivera, Beatriz Bellosillo, Josep Tabernero, Ramon Ramon Salazar, Enrique Aranda, Clara Montagut. Application of Liquid Biopsy-RECIST (LB-RECIST) criteria to track metastatic colorectal cancer (mCRC) molecular response in first-line (1L) setting: Findings from the PLATFORM-B study [abstract]. In: Proceedings of the AACR Special Conference: Liquid Biopsy: From Discovery to Clinical Implementation; 2024 Nov 13-16; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(21_Suppl):Abstract nr PR009.