Evaluation of alternative prognostic thresholds for SP142 and 22C3 immunohistochemical PD-L1 expression in triple-negative breast cancer: results from a population-based cohort

Abstract Background Immune checkpoint inhibitors are now a part of the treatment arsenal for triple-negative breast cancer (TNBC) but refinement of PD-L1 as a prognostic and predictive biomarker is a clinical priority. We aimed to evaluate the relevance of novel PD-L1 immunohistochemical (IHC) thresholds in TNBC with regards to PD-L1 gene expression, prognostic value, tumor infiltrating lymphocytes (TILs) and TNBC molecular subtypes. Material CPS) IHC assays and evaluated abundance of TILs in a population-based cohort of 237 early-stage TNBC patients. Survival analysis was performed and RNA sequencing data employed for molecular profiling. Results As expected, PD-L1 positivity (IC ≥1% and/or CPS ≥1) was significantly associated with better prognosis compared to zero PD-L1 expression. Importantly however, also patients with intermediate expression (IC >0%, 0, CD274) gene expression (mRNA). Patients that were both low in TILs (Conclusion With both SP142 and 22C3, we identified an intermediate IHC PD-L1 group within TNBCs that was supported on the molecular level. Any PD-L1 IHC expression, even though it is Trial Registration The Swedish Cancerome Analysis Network – Breast (SCAN-B) study was retrospectively registered 2nd Dec 2014 at ClinicalTrials.gov; ID NCT02306096.