Abstract P4-10-14: Quantitative assessment of PD-L1 protein expression on macrophages and tumor cells as predictive markers of response to neoadjuvant durvalumab and chemotherapy in triple negative breast cancer (TNBC)

Background: In the IMpassion 130 trial, TNBC patients treated with Atezolizumab and nab-Paclitaxel that showed immune cell expression of PD-L1 showed better overall survival. The goal of this analysis was to assess association between quantitative PD-L1 expression, in various tissue compartments, and pathologic complete response (pCR: ypT0/N0) to neoadjuvant anti-PD-L1 therapy concurrent with nab-paclitaxel (100 mg/m2) x 12 followed by ddAC x 4 chemotherapy in stage I-III triple negative breast cancer (TNBC). Methods: Pre-treatment core needle biopsies (n=69) were obtained from patients who participated in a Phase I/II clinical trial (NCT02489448). Of these 24 patients samples were excluded due to a range of clinical and technical issues. The final analysis had 45 patients (pCR = 18, non-pCR = 27). The slides were stained using a previously validated Ultivue DNA-based Ultimapper® kit (CD8, CD68, PD-L1, Cytokeratin/Sox10 and Hoechst counterstain for nuclear staining). Briefly, mouse monoclonal antibodies with a short DNA strand attached to the Fc region were amplified and attached with a complimentary DNA strand attached to a fluorophore followed by an amplification procedure. We stained 8 batches of slides with 2 control slides for each batch to assess for variability between batches (CD8, CD68 and PD-L1). The images were analyzed by molecular compartmentalization without segmentation using AQUA software (version 3.2.2.1) for each marker in different compartments (tumor, stroma and CD68 for PD-L1). A column graph and Mann-Whitney U-test was used to analyses the results for statistical significance between pCR and non-pCR. P-values shown are not adjusted for multiple comparisons. Results: Reproducibility between batches was excellent (CD68; R2 = 0.86 to 0.94 and PD-L1; R2 = 0.87 to 0.98). PD-L1 expression was significantly higher in the tumor compartment, the stromal compartment, and in the CD68 compartment in pCR patients compared to non-pCR. However, comparative analysis between the pCR and non-pCR patients showed no difference in the overall presence of CD68 in any of the molecular compartments. Conclusion: Expression of PD-L1 in tumor cells and immune cells in stroma and the CD68 expression compartment (predominantly macrophages) is associated with response to Durvalumab and chemotherapy in this small neoadjuvant TNBC trial. This result, the association of PD-L1 expression in macrophages with outcome, has also been seen in melanoma (Toki et al CCR 2019) and lung cancer (Liu et al, in revision). Further study is required to validate this potential predictive biomarker. Citation Format: Fahad Shabbir Ahmed, John McGuire, Patricia Gaule, Kim Blenman, Lajos Pusztai, David L Rimm. Quantitative assessment of PD-L1 protein expression on macrophages and tumor cells as predictive markers of response to neoadjuvant durvalumab and chemotherapy in triple negative breast cancer (TNBC) [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P4-10-14.