PD-L1 expression on circulating tumor cells and prognosis of breast cancer patients.

Abstract

e14028 Background: Nowadays programmed cell death (ligand) 1 (PD1/PD-L1) inhibitors in the clinic show benefit for appropriate patient. There are clinical trials for specific breast cancer patients. We all know that the prognosis of breast cancer is associated with CTC. However, PD-L1 expression on circulating tumor cells (CTC) is lack of research. It is crucial for the prediction and supervision of molecular-targeted therapy, while the predictive biomarker response to PD(-L)1 checkpoint inhibitors is lacking. So we tried to explore the relationship between overexpression of PD-L1 on CTCs and prognosis and clinicopathological features of breast cancer patients. Methods: We analyzed CTC and PD-L1 mRNA expression on CTC in 20 primary breast cancer patients, through mRNA probe hybridization. The relationship between clinicopathological features and PD-L1 expression on CTC was analyzed by chi square test. Kaplan-Meier and univariate Cox proportional hazards model analyses were used to compare the survival of patients with high PD-L1 expression and patients with low PD-L1 expression. Results: The median follow-up time was 40 months (range, 36-43 months). Of the 20 patients, 15 had more than 1 CTC in 7.5ml peripheral blood. Among the 15 patients, each one has at least 1 CTC showing PD-L1. The expression of PD-L1 on CTC was divided into low expression, medium expression and high expression, then we gave 1 score for low expression, 2 score for medium expression and 3 score for high expression. PD-L1 high expression was total score≥3, while PD-L1 low expression was total score ＜ 3. We found PD-L1 expression on CTC is related to the tumor size(P = 0.012) lymph node status (P = 0.001) and PR status (P = 0.037). There was significant difference between T2 and T3 in large tumor group(P = 0.003), while in node status group statistical difference can be found in N1 vs N3(P = 0.000) and N2 vs N3(P = 0.015). Our data indicated that patients with high PD-L1 expression on CTC had poor overall survival(P = 0.004) compared to low PD-L1 expression on CTC (Table). Univariate Cox proportional hazards model analysis showed that high PD-L1 expression on CTC was an independent prognostic factor. Conclusions: PD-L1 on CTC is indeed associated with some poor clinicopathological features. High expression of PD-L1 on CTC is an independent prognostic factor for shorter survival. [Table: see text]