Abstract PS4-38: Association of tumor infiltrating lymphocytes (TILs) density and PD-L1 expression with pembrolizumab (P) plus gemcitabine (Gem) efficacy in patients with HER2-negative advanced breast cancer (ABC) from the GEICAM/2015-04 (PANGEA-Breast) study
Background Immune cells (ICs) infiltration and immune checkpoints have been shown to be important for BC patients’ (pts) prognosis and response to immunotherapy. We aimed to analyze the relation between TILs prevalence and PD-L1 expression with efficacy to an immunostimulatory combination with P and Gem in ABC HER2-negative pts previously treated with ≤4 chemotherapy and/or ≥2 hormone therapy lines from the PANGEA-Breast trial (NCT03025880). Methods Pre-treatment (ttm) metastatic BC samples were assessed for TILs density [% of occupied stromal area upon H&E staining] and for PD-L1 immunohistochemistry expression using monoclonal anti-PD-L1 antibody clone 22C3 (Merck) by calculating ICs score (% of positive infiltrated ICs) and combined positive score [CPS; PD-L1 stained cells (tumor cells, lymphocytes, macrophages) divided by total viable tumor cells, multiplied by 100]. Cut-offs ≥5%, ≥10%, ≥30% were explored for TILs. PD-L1 scores were considered positive if ≥1%. Cut-offs (≥5%, ≥20%, ≥50%) were additionally assessed for PD-L1 as CPS. Logistic regression models were used to evaluate association between TILs density and PD-L1 expression with ttm efficacy in terms of Objective Response Rate [ORR; Complete + Partial Response (CR + PR)], Clinical Benefit Rate [CBR; CR + PR + Stable Disease ≥24 weeks] and Progression Free Survival (PFS), according to RECIST v1.1. Results Thirty-six pts were included, 58% had triple negative BC and 98% ECOG score ≤1. Median number of prior ttm lines was 4. ORR and CBR were 15.2% and 17%, respectively; median PFS was 3.1 months. TILs and PD-L1 were evaluated in 30 and 29 pts, respectively. No association was found between TILs density and ttm efficacy in terms of ORR, CBR and PFS. Analysis of PD-L1 ICs score did not reveal any significant association with ORR, CBR or PFS. However, pts with negative PD-L1 expression by CPS (Citation Format: Luis De la Cruz, María Gion, Josefina Cruz, Jose Luis Alonso, Vanesa Quiroga, Fernando Moreno, Marta Santisteban, Raquel Andrés, Esther Holgado, Natalia Palazón, Luz Milva Rodríguez, Asunción Soto, Javier Cortés, Alfonso Cortés, Manuel Ramos, Maribel Casas, Massimo Chiesa, Susana Bezares, Rosalía Caballero, Federico Rojo. Association of tumor infiltrating lymphocytes (TILs) density and PD-L1 expression with pembrolizumab (P) plus gemcitabine (Gem) efficacy in patients with HER2-negative advanced breast cancer (ABC) from the GEICAM/2015-04 (PANGEA-Breast) study [abstract]. In: Proceedings of the 2020 San Antonio Breast Cancer Virtual Symposium; 2020 Dec 8-11; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2021;81(4 Suppl):Abstract nr PS4-38.