Cancer-derived inflammation attenuates the efficacy of adjuvant chemotherapy (CT) in postoperative or metastatic colorectal cancer (mCRC). However, its role in mCRC patients receiving first-line Bevacizumab combined with chemotherapy (Bev/CT) remains unknown. In this prospective observational study, three Bev/CT regimen cohorts (discovery cohort,n=249; Internal validation cohort: n=115; external validation cohort: n=159) and one CT regimen cohort (n=175) were enrolled. Overall survival served as the primary endpoint; clinical response and progression-free survival were secondary endpoints evaluated during follow-up. Investigators used the serum inflammation ratios to evaluate the association between systemic inflammation and clinical outcomes in Bev/CT- and CT-treated mCRC. Combined analysis of 12 cytokines (flow cytometry) and 92 immuno-oncology proteins (Olink) revealed Bev resistance mechanisms and prognosis-predictive biomarkers in Bev/CT treated patients.

Inclusion Criteria:

• Clinical diagnosis of mCRC;
• Aged over 18 years;
• Must be able to receive the further treatment in the hospital.

Exclusion Criteria:

• More than two types of malignancies;
• Bacterial or virus infection within one month before diagnosis;
• Taken anti-inflammatory drugs or other forms of chemotherapy before their diagnosis;
• participants whose follow-up was interrupted three months ago without reaching any endpoint.

In this study, all enrolled patients received first-line CT or Bev/CT based on the decisions made by both patients and clinicians. The treatment regimens included: (1) oxaliplatin-based CT (FOLFOX/XELOX, OX), (2) irinotecan-based CT (FOLFIRI/ XELIRI, IRI), (3) Bev combined with oxaliplatin-based CT (Bev/OX), and (4) Bev combined with irinotecan-based CT (Bev/IRI). All the patients underwent at least two cycles of Bev/CT until they either withdrew from the disease, experienced disease progression, or encountered intolerable toxic effects.