Assessing the Clinical Relevance of Soluble PD-1 and PD-L1: A Multi-Cohort Study Across Diverse Tumor Types and Prognostic Implications

Abstract

Background/Objectives: Immune checkpoint inhibitors targeting the PD-1/PD-L1 pathway have revolutionized cancer immunotherapy, however the clinical relevance of their soluble forms (sPD-1 and sPD-L1) remains less studied. Soluble PD-1 and PD-L1 have been implicated in tumor progression, prognosis, and treatment response across various malignancies. This study aims to provide a comprehensive analysis of sPD-1 and sPD-L1 levels in serum across diverse tumor types, including rare malignancies, and to evaluate their associations with clinicopathological characteristics and prognostic significance. Methods: In this study we analyzed sPD-1 and sPD-L1 levels in serum samples from 675 cancer patients representing a range of malignancies, including ovarian cancer, breast cancer, gastric cancer, colorectal cancer, renal cell carcinoma, and bone tumors. sPD-1 and sPD-L1 concentrations were measured using ELISA. Statistical analyses were performed to evaluate associations between soluble marker concentrations and clinicopathological factors, including tumor stage, size, histological subtype, and survival outcomes. Results: Elevated sPD-L1 levels were observed in several tumor types, including ovarian cancer, renal cell carcinoma, and gastric cancer, where they were associated with features of advanced disease, such as tumor size, stage, and metastases. In contrast, sPD-1 levels showed limited associations, with significant findings solely in gastric cancer and bone tumors, where levels correlated with histological subtype and differentiation. Prognostic analyses identified sPD-L1 as a marker of poor survival outcomes in ovarian cancer and bone tumors, while sPD-1 displayed no consistent prognostic significance. Conclusions: This study identifies the potential of sPD-L1 as a biomarker for tumor progression and prognosis across multiple malignancies. In contrast, sPD-1 showed limited clinical relevance, suggesting the importance of further investigation. These findings contribute to our understanding of soluble immune checkpoint proteins and their integration into personalized oncology strategies.

Keywords: cancer biomarkers; prognosis; sPD-1; sPD-L1; tumor progression.

Figure 1

Comparison of serum levels of sPD-1 and sPD-L1 between patients with malignant tumors and healthy controls. Serum levels of sPD-1 and sPD-L1 were measured using ELISA and compared across different malignancies and healthy controls. sPD-1 levels were significantly lower in gastric and breast cancer patients compared to healthy controls but higher in renal cancer patients. In contrast, sPD-L1 levels were significantly elevated in all tumor groups except colorectal cancer. Notable differences were observed in female-specific cancers, with breast and ovarian cancer patients showing significantly higher sPD-L1 levels than healthy women. Lines represent median values.

Figure 2

Receiver Operating Characteristic (ROC) curves for the diagnostic performance of sPD-1 and sPD-L1 levels in various malignancies. ROC analysis demonstrated the ability of serum sPD-1 and sPD-L1 levels to differentiate malignant from non-malignant cases across tumor types. sPD-1 shows excellent diagnostic accuracy in breast and gastric cancer, while sPD-L1 demonstrates moderate performance in breast and ovarian cancer. In other malignancies, both biomarkers exhibit low or no diagnostic value. The AUC values reflect the variable discriminatory power of these immune checkpoint molecules across different cancers. Red line indicates line of no discrimination, black line—receiver operating characteristic curve.

Figure 3

Heatmap summarizing statistical significance of associations between serum sPD-1 and sPD-L1 levels with clinicopathological characteristics across different tumor types. The heatmap represents the statistical significance of associations between serum sPD-1 and sPD-L1 levels and various tumor characteristics, including histological subtypes, stage, tumor size, nodal status, metastasis, and grade. Different tumor types are compared, highlighting variations in biomarker expression across malignancies. The color intensity reflects the strength of statistical significance, providing an overview of the tumor-specific patterns of sPD-1 and sPD-L1 regulation.

Figure 4

Overall survival (OS) analysis based on serum levels of sPD-1 and sPD-L1 across various malignancies. Kaplan–Meier survival curves show that high serum sPD-L1 levels are associated with significantly worse OS in renal cell carcinoma, ovarian cancer, and bone tumors. In contrast, sPD-1 levels generally do not impact OS, except in bone tumors, where lower levels are linked to a slightly improved prognosis. No significant associations were observed for gastric or colorectal cancer. *—statistically significant.

Figure 4

Overall survival (OS) analysis based on serum levels of sPD-1 and sPD-L1 across various malignancies. Kaplan–Meier survival curves show that high serum sPD-L1 levels are associated with significantly worse OS in renal cell carcinoma, ovarian cancer, and bone tumors. In contrast, sPD-1 levels generally do not impact OS, except in bone tumors, where lower levels are linked to a slightly improved prognosis. No significant associations were observed for gastric or colorectal cancer. *—statistically significant.

Figure 5

Correlation analysis of serum sPD-1 and sPD-L1 levels across various malignancies and healthy controls. A significant positive correlation was observed in colorectal cancer. In contrast, gastric cancer and breast cancer exhibited strong negative correlations. No significant correlation was found in ovarian cancer, RCC, bone tumors and healthy donors. *—statistically significant.