BACKGROUND: A small proportion of patients with advanced esophageal squamous 
cell carcinoma (ESCC) could benefit from immune checkpoint inhibitors; however, 
reliable peripheral blood biomarkers for outcomes of anti-PD-1 immunotherapy in 
ESCC have not been identified.
METHODS: The data of 43 patients in the ESCC cohort of a phase I trial at our 
center were retrospectively reviewed. All patients were administered intravenous 
camrelizumab (SHR-1210), a novel anti-PD-1 antibody, at doses of 60 mg, 200 mg, 
or 400 mg (4-week interval after first dose followed by a 2-week schedule) until 
disease progression or intolerable toxicity. Associations between lactate 
dehydrogenase (LDH) and other peripheral blood biomarkers at baseline and the 
efficacy of camrelizumab were also investigated.
RESULTS: After median follow-up of 19.6 months, the overall response rate was 
25.6% (11/43), including one complete response. Median progression-free and 
overall survival rates were 2.0 and 8.0 months, respectively. Patients with an 
elevated baseline LDH had lower tumor response rates (P = 0.02) and shorter 
progression-free (P = 0.002) and overall (P < 0.0001) survival than patients 
with normal LDH levels. An increase in LDH levels during treatment was 
significantly associated with disease progression. Multivariate Cox analysis 
identified LDH (hazard ratio [HR] 0.18), CRP (HR 0.27), the number of organs 
involved (HR 0.31), absolute monocyte count (HR 0.33), and Eastern Cooperative 
Oncology Group performance status (HR 0.36) as independent prognostic factors.
CONCLUSIONS: Serum LDH, which is readily available in routine clinical practice, 
is a potential marker for response and a powerful independent factor for 
survival in advanced ESCC patients treated with anti-PD-1 therapy.