Today there has been an outbreak progress in immunotherapy for tumors, where immune checkpoint inhibitors targeting PD-1/PD-L1 have been approved for the treatment of a variety of tumors, bringing long-term benefits to some patients, especially colorectal cancer and other solid tumors with dMMR/MSI-H have been identified as the best indication population for immunotherapy. However, the majority of patients presented with microsatellite stable (MSS) or pMMR status had a low response rate to immunotherapy. How to improve the response to immunotherapy in these patients has been a challenge in the field of colorectal cancer immunotherapy. A number of preclinical and small clinical studies have identified immunotherapy in combination with other treatments such as chemotherapy, radiotherapy, anti-angiogenic drugs and targeted therapies as potentially viable options to overcome immune resistance and improve the outcome of MSS colorectal cancer. Preclinical and small clinical studies have demonstrated that radiotherapy may induce antigen release from tumors with low neoantigen load and activate dendritic cells, thereby activating CD8+ T lymphocyte-mediated anti-cancer immune responses. In patients with locally advanced rectal cancer, neoadjuvant chemoradiotherapy can increase PD-L1 expression in tumor cells, suggesting that the combination of radiotherapy and PD-1/PD-L1 inhibitors may have a synergistic effect. To further improve the treatment outcomes of locally advanced rectal cancer, we designed an exploratory observational study to observe the efficacy and safety of a regimen of short-course radiotherapy combined with chemotherapy and the addition of the PD-1 monoclonal antibody in locally advanced rectal cancer, and to initially explore the feasibility a watch-and-wait strategy for patients with rectal cancer who have reached pCR.
The goal of this phase 2 study is to learn about the efficacy and safety of short-course radiotherapy (SCRT) sequential Penpulimab in combination with CAPEOX in the neoadjuvant treatment of microsatellite stable (MSS) locally advanced rectal cancer. The main question it aims to answer is the role of immune checkpoint inhibitors in the neoadjuvant treatment of MSS rectal cancer. Participants will receive neoadjuvant treatment of SCRT sequential Penpulimab in combination with CAPEOX. Participants will undergo a clinical re-staging assessment at the end of neoadjuvant therapy to determine whether to adopt a watch-and-wait strategy or undergo radical surgery.