RecruitingDrug trialCombination Immunotherapy for the Treatment of Chemotherapy-refractory Metastatic MSS CRCPhase 1b/2 open-label study evaluates the safety, tolerability, and efficacy of combination immunotherapy with nadunolimab (anti-IL-1RAP) and toripalimab (anti-PD-1) in patients with chemotherapy-refractory metastatic microsatellite stable (MSS) colorectal cancer. Phase 1b will assess dose-limiting toxicity (DLT), while Phase 2 will evaluate objective response rate (ORR), including progression-free survival (PFS), overall survival (OS), disease control rate (DCR), and duration of response (DOR). Exploratory analyses will investigate immunomodulatory effects through tumor and peripheral blood studies, and treatment will continue every 3 weeks for up to 1 year or until disease progression.