Chemoradiotherapy and Anti-PD-1 Antibody in Anal Squamous Cell Cancer：Chase

Squamous cell carcinoma (SCC) of the anus is a rare malignancy. For localized anal squamous cell carcinoma , definitive chemoradiotherapy is the standard treatment. Patients who do not achieve complete response （CR）or experience recurrence require radical surgery with permanent colostomy. In previous studies of anal squamous cell carcinoma （ASCC）, although favorable response rates were achieved after concurrent chemoradiotherapy, high rates of local recurrence and distant metastasis were also observed in patients with locally advanced disease, which adversely affect patient survival. Clinical studies have demonstrated that single-agent PD-1/PD-L1 inhibitors, including nivolumab and pembrolizumab, show promising efficacy in advanced anal squamous cell carcinoma. Given the high recurrence rate associated with current concurrent chemoradiotherapy regimens and the characteristics of the immune microenvironment in anal cancer, the combination of immunotherapy with concurrent chemoradiotherapy is expected to improve therapeutic outcomes. Therefore, we designed this prospective, multicenter, phase II clinical study to investigate the efficacy and safety of concurrent chemoradiotherapy combined with immune checkpoint inhibitors in anal cancer. This study aims to enhance the therapeutic effect for patients with locally advanced, recurrent, or metastatic anal squamous cell carcinoma and reduce adverse events in patients with high-risk factors after local excision or in early-stage disease. The primary endpoints are local tumor control rate, overall survival, and radiation-related toxicity. The results will provide evidence for subsequent randomized controlled trials.