Background: Moving stage III Colon Cancer (CC) into the precision medicine space is a priority in view of the lack of molecular markers driving adjuvant treatment. Retrospective studies have demonstrated the tremendous prognostic impact of circulating tumor DNA (ctDNA) analysis after curative intent surgery, and suggested that lack of conversion of ctDNA from detectable to undetectable after adjuvant chemotherapy reflects treatment failure. With these premises, we have designed the PEGASUS trial (EudraCT 2019-002074-32) to prove the feasibility of using liquid biopsy to guide the post-surgical and post-adjuvant clinical management of early colon cancer patients.

Methods: PEGASUS is a prospective multicentric vanguard study designed to test the feasibility of performing serial interventional liquid biopsies (LB) for ctDNA determination in 140 microsatellite stable Stage-III and T4N0 Stage-II CC patients. The LUNAR1 (Guardant Health, Redwood City, CA, USA) will be used for ctDNA determination. For the efficacy analysis, the PEGASUS cohort will be compared with a cohort of 420 patients from the TOSCA trial (NCT00646607) population matched 3:1 for all known prognostic phenotypes. A post-surgical LB executed 2-4 weeks after surgery will guide a “Molecular Adjuvant” treatment as follows: i) ctDNA+ patients will receive CAPOX for 3 months and ii) ctDNA- patients will receive capecitabine (CAPE) for 6 months but will be retested after 1 cycle, and if found ctDNA+ will be switched to CAPOX treatment. Immediately after the end of “Molecular Adjuvant” treatment a further LB will be performed and instruct subsequent treatment. Positive patients (ctDNA+/+ and ctDNA-/+) will receive an up-scaled “Molecular Metastatic” systemic treatment for 6 months or until radiological progression or toxicity as follows: i) ctDNA+/+ patients will be treated with FOLFIRI; ii) ctDNA-/+ patients with CAPOX. These patients will be subjected to a LB after 3 months and at the end of treatment and in case of positivity will be switched to FOLFIRI. Patients experiencing ctDNA conversion to negative (ctDNA+/-) will receive a de-escalated treatment with CAPE for 3 months. 3 LB will be performed within 3 months and in case of positivity the patient will be switched to FOLFIRI. Patients with ctDNA-/- will be subjected to an interventional follow-up comprising 2 further LB and in case of positivity they will be switched to CAPOX treatment. PEGASUS is piggybacked to AlfaOmega (NCT04120935), a Master Observational Protocol that will follow patients from diagnosis to 5 years or recurrence/death (whichever comes first), collecting clinical data, radio images and biological samples. AlfaOmega provides a clinical and logistic ecosystem for the seamless integration of PEGASUS clinical results with the biological underpinning of colon cancer.

Citation Format: Elena Elez, Filippo Pietrantonio, Andrea Sartore-Bianchi, Clara Montagut, Andres Cervantes, Stefania Sciallero, Maria Giulia Zampino, Stefania Mosconi, Valter Torri, Noelia Tarazona, Luca Lazzari, Paolo Luraghi, Susana Muñoz, Matteo Fassan, Enzo Medico, Livio Trusolino, Maria Rescigno, Salvatore Siena, Alberto Sobrero, Roberto Labianca, Josep Tabernero, Alberto Bardelli, Sara Lonardi, Silvia Marsoni. Post-surgical liquid biopsy-guided treatment of stage III and high-risk stage II colon cancer patients: The PEGASUS trial [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr CT263.