Abstract
Introduction: PD-1 inhibitors have been approved for the treatment of dMMR patients with metastatic colorectal cancer, but the efficacy of neoadjuvant treatment with PD-1 in dMMR locally advanced rectal cancer (LARC) patients has not yet been defined. Patients and methods: Two patients with LARC received Nivolumab as neoadjuvant treatment in July 2017. Whole-exome sequencing (WES) and multiplex immunofluorescence analysis were performed. Results: Of the two patients, one achieved pathological complete response after six cycles of nivolumab followed by surgery. The other patient was confirmed to be clinical complete response after six cycles of nivolumab. "Watch and wait" strategy was performed for anal preservation. WES showed high tumor mutation burden. Multiplex immunofluorescence analysis showed immune microenvironment alternation between pretreatment specimen and post-treatment specimen. Conclusion: Neoadjuvant nivolumab induced complete response in both of the two patients with LARC. Immunotherapy might be an alternative strategy for neoadjuvant treatment for dMMR/MSI rectal cancer.