Abstract P6-04-04: Clinical Relevance of PD-L1 and CD8 Expression in Triple Negative Breast Cancer

Abstract Background: Immune checkpoint inhibitors such as PD-L1 are promising therapy targets in triple negative breast cancer (TNBC). In the present study, we examined the clinical relevance of PD-L1 and CD8 expression in TNBC patients treated with adjuvant chemotherapy. Methods: FFPE tumor material from 118 patients with early TNBC treated between 1999 and 2012 was included in our analysis. Immunohistochemical (IHC) expression of PD-L1 was determined by immune score using the diagnostic antibody SP142 (Ventana). CD8 IHC was performed using the SP57 antibody (Ventana). Follow-up data were available for all 118 patients with a median follow up time of 19.4 years. Biomarkers were examined as continuous or categorical variable (predefined cutoffs). Invasive disease-free survival (IDFS) and overall survival (OS) were analyzed using Cox regression models. Results: The median PD-L1 immune score was 1% and PD-L1 expression was classified as positive in 79/116 (68.1%, cutoff ≥1%) cases. Median CD8 expression was 10% and was scored as positive in 51/115 (44.3%, cutoff >10%) samples. Significant associations were observed between PD-L1 expression and tumor grade, Ki67, and CD8 expression. PD-L1-positive tumors were more frequently in the G3 group (p=0.006) and had higher Ki67 (p< 0.001) and higher CD8 expression (p< 0.001). PD-L1 but not CD8 expression was associated with IDFS or OS. Univariate Cox regression analyses showed that PD-L1-negative patients had a shorter IDFS (HR 0.52, 95%CI 0.30-0.89, p=0.02) and showed a trend towards shorter OS (HR 0.56, 95%CI 0.30-1.03, p=0.06). CD8 expression was neither associated with IDFS (HR 0.74, 95%CI 0.43-1.27, p=0.27) nor with OS (HR 0.87, 95%CI 0.48-1.60, p=0.66). In multivariate analyses, PD-L1 expression was an independent prognostic factor for IDFS (HR 0.51, 95%CI 0.29-0.88, p=0.016) but not for OS (HR 0.53, 95%CI 0.28-1.01, p=0.052). Conclusions: Our results suggest that PD-L1 but not CD8 expression assessed by IHC predicted outcome in TNBC. Further analysis of larger, suitable patient cohorts is warranted to further assess the prognostic and predictive value of PD-L1 expression. Citation Format: Zsuzsanna Bago-Horvath, Maximilian Marhold, Ulrike Heber, Rupert Bartsch, Florian Fitzal, Christian F. Singer, Martin Filipits. Clinical Relevance of PD-L1 and CD8 Expression in Triple Negative Breast Cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P6-04-04.