Clinical Impact of PD-L1 Expression in Triple Negative Breast Cancer Patients With Residual Tumor Burden After Neoadjuvant Chemotherapy

Abstract Background: Studies on PD-L1 expression in breast cancer have gained importance in recent years, especially in triple negative breast cancer (TNBC). Our aim was to analyse the differential expression of PD-L1 to explore its correlation with response to neoadjuvant chemotherapy (NACT) and patient survival. Methods: PD-L1 expression was evaluated immunohistochemically (Ventana SP263 clone kit) by staining tumor specimen. PD-L1 positivity was defined as membranous staining >1%, >5%, >10% and >20% on either tumor cell (TC) and /or immune cell (IC). Results: Fifty patients with locally advanced TNBC, who had a partial response to NACT, were included in the study. Twenty-nine patients (58%) were detected to be positive for PD-L1 on both TCs and ICs, whereas 25 patients (50%) were positive for TC PD-L1 expression, and PD-L1 on ICs was detected (44%) in 23 patients. Patients with PD-L1 positivity on ICs were more likely to respond to chemotherapy as measured by “MD Anderson Cancer Center Residual Cancer Burden Index” (14/22, 63.6%, versus 10/27, 37%, p = 0.064). The 5-year disease-free survival (DFS) and disease-specific survival (DSS) rates were 46.3% and 51.4%, respectively. A high (>20%) tumoral PD-L1 positivity was associated with a better DFS and DSS. Conclusions: Our results suggest that patients with a high TC PD-L1 expression were more likely to have a better outcome. Since patients with residual TCs expressing PD-L1 on TILs were more likely to respond to NACT, an immune checkpoint inhibitor therapy in addition to NACT would be an important option for TNBC with locally advanced disease.