PD-L1 Protein Expression on Both Tumor Cells and Macrophages are Associated with Response to Neoadjuvant Durvalumab with Chemotherapy in Triple-negative Breast Cancer

Purpose: In both the IMpassion 130 trial in the metastatic setting and in Keynote 522 in the neoadjuvant setting, patients with triple-negative breast cancer (TNBC) showed benefit from PD-1 axis immunotherapy. Here, we assess PD-L1 expression on both tumor and immune cells using quantitative immunofluorescence to assess association with benefit from neoadjuvant durvalumab concurrent with chemotherapy in TNBC. Experimental Design: Pretreatment core needle biopsies (n = 69) were obtained from patients who participated in a phase I/II clinical trial (NCT02489448). The final analysis included 45 patients [pathologic complete response (pCR) = 18, non-pCR = 27] due to technical issues and insufficient tissue. Slides were stained using a previously validated Ultivue DNA-based Ultimapper kit (CD8, CD68, PD-L1, Cytokeratin/Sox10, and Hoechst counterstain). The PD-L1 expression was analyzed by molecular compartmentalization without segmentation using AQUA software (version 3.2.2.1) in three tissue compartments including tumor (cytokeratin-positive cells), CD68+ cells, and overall stroma. Results: In patients with pCR, PD-L1 expression was significantly higher in tumor cells, in CD68+ cells and in the stroma compared with patients non-pCR. There was no difference in the amount of CD68+ cells in the tumor or stromal compartments between cases with pCR and non-pCR. Conclusions: Expression of PD-L1 in tumor cells, immune cells in stroma, and colocalized with CD68+ cells is associated with higher rates of pCR to durvalumab and chemotherapy in TNBC.