The Clinicopathological and Prognostic Significance of the Expression of PD-L1 and MET Genes in Breast Cancer: Potential Therapeutic Targets.

Introduction: The heterogeneity of breast cancer requires exploring novel prognostic biomarkers as well as therapeutic targets for the treatment of the disease.

Methods: The METABRIC dataset was used to describe the gene expression of the programmed death-ligand 1 (PD-L1) and the hepatocyte growth factor receptor (MET) and their association with the tumor clinicopathologic characteristics and overall survival in breast cancer.

Results: The expression of the PD-L1 and MET genes correlated positively with the Nottingham Prognostic Index (NPI) (p=0.003 and p < 0.001, respectively). The expression of the two genes correlated inversely with luminal A and luminal B tumors (r= - 0.089, p= 0.021 and r= - 0.116, p= 0.013, respectively). The PD-L1 mRNA levels were significantly higher in hormone receptor-negative and HER2-positive tumors. MET mRNA expression levels were significantly higher in hormone receptor-negative, HER2-enriched, and non-luminal breast cancers. The PD-L1/MET double-high expression was associated with younger age of patients at diagnosis, higher NPI scores, larger tumors, advanced stage, high-grade, hormone receptor-negativity, HER2-positivity, and non-luminal tumors. None of the genes or their double expression status was significantly associated with overall survival in this analysis.

Conclusion: The expression of the PD-L1 and MET genes is remarkably associated with worse tumor clinicopathologic features and poor prognosis in patients with breast cancer. Further investigations using combination drug regimens targeting PD-L1 and MET are important, particularly in breast tumors expressing high levels of both proteins.