Cell division cycle 42 (CDC42) regulates immune escape, which predicts immune checkpoint inhibitor (ICI) treatment response in several types of cancer. The present study aimed to evaluate the potential of serum CDC42 in predicting the ICI treatment outcome in patients with advanced cervical cancer. A total of 46 patients with advanced cervical cancer who received ICI treatment with or without antiangiogenic agents were enrolled. Serum CDC42 was detected in all patients before treatment (baseline) and following two treatment cycles by enzyme-linked immunosorbent assay. CDC42 at baseline was elevated in patients with target lesion size ≥5 cm (P=0.020), pelvis metastasis (P=0.031) and lung metastasis (P=0.043). Following treatment, the objective response rate (ORR) and disease control rate (DCR) were 30.4 and 78.3%, respectively. Meanwhile, the median progression-free survival (PFS) and overall survival (OS) were 5.8 and 13.1 months. CDC42 at baseline was decreased in patients achieving ORR (P=0.042) but not DCR (P=0.055). PFS (P=0.006) and OS (P=0.019) were decreased in patients with baseline CDC42 ≥600 pg/ml. After two treatment cycles, CDC42 was generally reduced (P<0.001). CDC42 following two treatment cycles was more significantly decreased in patients with ORR (P=0.032) and DCR (P=0.019). Multivariate Cox's regression analysis showed that CDC42 ≥600 pg/ml following two treatment cycles was associated with the shorter PFS (P=0.022, hazard ratio=2.469) and OS (P=0.013, hazard ratio=4.166). Serum CDC42 was reduced after treatment; high expression following treatment reflected a lower possibility of achieving treatment response and poorer survival in patients with advanced cervical cancer.Copyright: © Guo et al.