To investigate the classification of programmed death-ligand 1 (PD-L1) in the circulating tumor cells (CTCs) of peripheral blood and its relationship with the clinicopathologic feature of patients with primary liver cancer (PLC).

Clinical data of 30 PLC patients admitted to Sun Yat-sen Memorial Hospital of Sun Yat-sen University from January 2017 to December 2019 were retrospectively analyzed. The informed consents of all patients were obtained and the local ethical committee approval was received. Among them, 27 patients were male and 3 female, aged 29-77 years with a median age of 51 years. The classifications of CTCs in the peripheral blood and the corresponding expression level of PD-L1 were determined by multiple RNA in situ analysis. The correlation between PD-L1 expression and clinicopathologic feature was analyzed by Chi-square test or Fisher's exact probability.

A total of 275 CTCs were detected, including 82 epithelial-type CTCs, 51 interstitial-type CTCs and 142 mixed-type CTCs. The average expression level of PD-L1 in the mixed-type CTCs was 0.89, significantly higher than 0.55 in the epithelial-type and 0.49 in the interstitial-type CTCs. The number of PLC patients with mixed-type CTCs and their expression level of PD-L1 were also significantly higher than those with other phenotypes. The classification of CTCs with positive PD-L1 was significantly associated with liver cirrhosis and liver capsule invasion (χ2=9.707, 7.153; P<0.05). The average expression level of PD-L1 in PLC patients was only correlated with the history of alcohol drinking (P=0.042).

The classification of CTCs in PLC patients is mainly mixed-type. Its expression level PD-L1 is higher than those with other phenotypes. The classification of PD-L1-positive CTCs is associated with liver cirrhosis and liver capsule invasion, whereas PD-L1 expression level is only correlated with the alcohol drinking history of PLC patients.