4051 Background: PD-1 blockade may result in expansion of tumor-specific T cells. However, traditional immunochemotherapy regimens usually designed to use chemotherapy drugs and anti-PD-1 antibody on the same day, which may make chemotherapy drugs kill activated T cells. The purpose of this study was to investigate the rate of pCR of chemotherapy plus anti-PD-1 therapy and the influence of sequence of chemotherapy and anti-PD-1 therapy on pCR in patients with locally advanced esophageal squamous cell cancer. Methods: Thirty esophageal squamous cell cancer patients with T3, T4, or lymph node positive were assigned into experiment group (anti-PD-1 antibody was administrated two days after chemotherapy) and control group ( anti-PD-1 antibody and chemotherapy were administrated on the same day) according to the order of enrollment. There were fifteen patients in each group. The chemotherapeutic regimen was paclitaxel and cisplatin, paclitaxel was given at the dose of 150-175mg/m2 on day 1 and cisplatin was given at the dose of 70-75mg/m2 on day 1. The anti-PD-1 antibody was toripalimab at the fixed dose of 240mg on day 3 or day 1. Operation was performed four to six weeks after the second cycle of chemotherapy combined with toripalimab. Results: From July 2019 to September 2020, a total of 30 patients completed at least one cycle of immunochemotherapy. 11 in the experimental group received operation after two cycles of neoadjuvant chemotherapy plus toripalimab. Thirteen in control groupreceived operation aftertwo cycles of neoadjuvant chemotherapy plus toripalimab. Four patients in experimental group and one in control group got pCR, the rates of pCR in experimental group and control group were 36.4% and 7.7% individually. Although the difference was not significant in statistics, the experimental group had the trend of higher pCR rate(c2= 3.092, p = 0.079). PD-L1 CPS examination before treatment was performed in fourteen patients, it was found that except one patient with PD-L1 CPS was 10, the left thirteen with PD-L1 CPS were all below one. The patient with PD-L1 CPS 10 was in control group and pCR was got in this patient. Except one patient in the experimental group had grade 3 immune-related enteritis, one patient in the control group died from immune-related myocarditis after operation, there were no more immune-related events more than grade 3. Conclusions: Toripalimab was delayed on day 3 when toripalimab plus chemotherapy was taken as neoadjuvant therapy regimen in locally advanced esophageal squamous cell carcinoma might achieve a higher pathological complete response than toripalimab and chemotherapy used on the same day. Clinical trial information: NCT 03985670.
978P A prospective study of camrelizumab monotherapy following definitive concurrent chemoradiotherapy in patients with unresectable locally advanced esophageal squamous cell cancer
