Evaluation of the Efficacy and Safety of Bevacizumab Combined With PD-1 Monoclonal Antibody in Preoperative Neoadjuvant Therapy for MSS Colorectal Cancer With Liver Metastases

In the 2023 Global Cancer Statistics, colorectal cancer remains the third leading cause of cancer-related death in the world. According to the latest China Cancer report, colorectal cancer is the fourth leading cause of cancer-related death in China. More specifically, the incidence and the mortality of colorectal cancer have been increasing year over year. Among newly diagnosed colorectal cancer patients, 20% have distant metastases. The 5-year survival rate for metastatic colorectal cancer (mCRC) is less than 20%. In the latest updated 2023 National Cancer Comprehensive Network (NCCN) Colon Cancer Guidelines, mismatch repair genes/micro satellite state officially became a global classification standard. Patients diagnosed with colorectal cancer must be classified into MSS or MSI-H before treatment, that is, patients are divided into pMMR/MSS and dMMR/MSI-H subtypes after initial examination or clinical management, and then the treatment plan is determined. MSI-H accounts for 15% of all colorectal cancers and is mostly present in patients with early stage tumors. For patients with metastatic colorectal cancer, MSI-H colorectal cancer accounts for only 5% of all patients. Among them, the treatment of immune checkpoint inhibitors in MSI-H patients has become a first-line and neoadjuvant metastatic disease treatment recommendation.

Although clinical trials on the combination of targeted therapy and immunotherapy are increasing, clinical researches and clinical trials of targeted therapy combined immunotherapy, such as bevacizumab combined with PD-1, have not received enough attention and recognition. Currently reports believed that anti-programmed death-1 (PD-1) antibodies have been shown to produce significantly longer progression-free survival with fewer adverse events compared to chemotherapy as a first-line treatment for dMMR metastatic CRC (mCRC). In the simultaneous CRT sequential PD-1 (long range) and TNT simultaneous combined PD-1 (long range) clinical trials, CRT combined with PD-1/PD-L1 showed better near-term efficacy gains (pCR) in patients with locally staged pMMR. Although current researches on neoadjuvant therapy for MSS type bowel cancer is increasingly abundant, especially PD-1 is becoming more and more popular in the treatment of MSS type bowel cancer, the research in the field of neoadjuvant therapy for MSS metastatic colorectal cancer is still not explored. Therefore, our PD-1 combined with bevacizumab in the treatment of MSS type metastatic bowel cancer has greatly research value.

Based on the above reasons, we designed this study to observe the efficacy and safety of the target-free combination therapy regimen of PD-1 combined with bevacizumab for patients with MSS metastatic colorectal cancer, and strive to provide a high-level evidence-based basis for neoadjuvant therapy regimen for patients with MSS metastatic colorectal cancer.