Abstract 28: Prognostic value of baseline and early changes of circulating cell-free (cf)DNA in the neoadjuvant setting of early stage colon cancer (CC)

Abstract Introduction Circulating tumour (ct)DNA is an indicator of minimal residual disease and negative prognostic factor in stage II-III CC treated with surgery +/- adjuvant chemotherapy. No study, however, has ever analysed the prognostic value of this biomarker in CC patients (pts) treated with neoadjuvant chemotherapy. We sought to evaluate the prognostic value of baseline and early, on-treatment changes of cfDNA and ctDNA in stage II-III CC pts who were treated with one cycle of neoadjuvant FOLFOX chemotherapy followed by surgery +/- adjuvant FOLFOX chemotherapy in the PePiTA trial. Methods PePITA was a multicentre, single-arm, prospective phase II trial aiming to test in vivo tumour chemosensitivity as assessd by metabolic response using 18F-FDG PET/CT scan of early stage CC and to evaluate its association with survival outcome (NCT00994864). Plasma samples were prospectively collected at baseline and 2 weeks (ie, after one cycle of neoadjuvant FOLFOX chemotherapy). cfDNA was isolated with the QIAmp circulating nucleic acid kit (Qiagen), and quantified with the Qubit fluorometer (Life-Technologies). cfDNA samples were bisulfite converted using the EZ DNA Methylation-Gold™ Kit (Zymo Research), with NPY and WIF1 being selected as universal methylation markers for ctDNA and analysed with digital droplet (dd)PCR technology. Data from ddPCR were processed with the QuantaSoft V1.6 software (BioRad). The primary outcome measure was 3-year disease-free survival (DFS). Receiver operating characteristics curve analyses, Kaplan-Meier method, cox proportional hazards models and log-rank tests were used. Statistical analyses were carried out with the SPSS for MacOS version 25.0 (SPSS Inc). Results 80 pts were included (ypStage I-II 56%, ypStage III 44%). After a median follow-up of 52.5 months, 3-year DFS was 80% (95%CI 71.2-90.8) and 5-year OS 84% (95%CI 75.2-94.9). Pts with high (≥1.2 ng/µl) baseline cfDNA level had worse 3-year DFS (48% vs 80%; HR 2.72, 95%CI 1.02-7.25; p=0.036) and 5-year OS (71% vs 90%; HR 5.36, 95%CI 1.14-25.28; p=0.017) than those with low baseline cfDNA level. In a multivariable analysis (including sex, ypStage and CEA), baseline cfDNA was the only factor showing a trend towards statistical significance (HR DFS 2.6, 95%CI 0.96-7.01; p=0.059; HR OS 4.65, 95%CI 0.97-22.32; p=0.055). Early changes of cfDNA (Δ ≥11%) after one cycle of neoadjuvant FOLFOX chemotherapy failed to predict survival (HR DFS 1.08, 95%CI 0.42-2.81; p=0.873; HR OS 0.68, 95%CI 0.19-2.39; p=0.543). ctDNA analyses are ongoing and will be presented at the meeting. Conclusions For the first time, we have shown that baseline cfDNA may predict survival outcome in early stage CC pts treated with neoadjuvant chemotherapy. Pending confirmation in larger series, testing for cfDNA at baseline could help select high-risk pts who may benefit from neoadjuvant, FOXTROT-like, treatment strategies. Citation Format: Giacomo Bregni, Elena Trevisi, Chiara Senti, Andrea Pretta, Caroline Vandeputte, Pashalina Kehagias, Elena Acedo Reina, Amélie Deleporte, Paraskevas Gkolfakis, Jean-Luc Van Laethem, Philippe Vergauwe, Marc Van den Eynde, Guido Deboever, Jos Janssens, Gauthier Demolin, Stephane Holbrechts, Marylene Clausse, Thierry De Grez, Marc Peeters, Lionel D'Hondt, Karen Geboes, Tatiana Besse-Hammer, Alexis Buggenhout, Françoise Rothé, Patrick Flamen, Alain Hendlisz, Francesco Sclafani. Prognostic value of baseline and early changes of circulating cell-free (cf)DNA in the neoadjuvant setting of early stage colon cancer (CC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 28.