Programmed death-ligand 1 expression in the tumour stroma of colorectal liver oligometastases and its association with prognosis after liver resection.

Background: The clinical value of programmed death-ligand 1 (PD-L1) expression in colorectal liver oligometastases (CLOs) remains undefined. This study aimed to detect PD-L1 in the microenvironment of CLOs and determine its association with patient prognosis.

Methods: We collected 126 liver-resection specimens from CLO patients who underwent curative liver resection between June 1999 and December 2016. Immunohistochemistry (IHC) was performed to assess PD-L1 expression in paraffin-embedded specimens. Overall survival (OS) and recurrence-free survival (RFS) were analysed using the Kaplan-Meier method and log-rank test.

Results: PD-L1 was mainly expressed in the stroma of liver oligometastases. Patients with high PD-L1 expression had a higher proportion of clinical-risk scores (CRSs) of 2-4 (67.7% vs 40.4%; =0.004). With a median 58-month follow-up, patients with high PD-L1 expression had a significantly lower 3-year OS rate (65.5% vs 92.7%; =0.001) and 3-year RFS rate (34.7% vs 83.8%; <0.001) than patients with low PD-L1 expression. Multivariate Cox analysis demonstrated that high PD-L1 expression (hazard ratio [HR] = 3.581; 95% confidence interval [CI] 2.301-9.972; =0.015), CRS 2-4 (HR = 6.960; 95% CI 1.135-42.689; =0.036) and increased preoperative CA19-9 (HR = 2.843; 95% CI 1.229-6.576; =0.015) were independent risk factors for OS. High PD-L1 expression (HR = 4.815; 95% CI 2.139-10.837; <0.001) and lymph-node metastasis (HR = 2.115; 95% CI 1.041-4.297; =0.038) were independent risk factors for RFS.

Conclusion: This study found that PD-L1 was commonly expressed in the tumour stroma of CLOs and high PD-L1 expression was associated with poor prognosis.