Prognostic value of PD-L1 gene expression with Recurrence Score and 70-gene signature in patients with ER+/HER2- early breast cancer.

Abstract

550 Background: We have previously demonstrated that PD-L1 mRNA expression can serve as prognostic biomarker in breast cancer (BC). In ER+/HER2- BC, RS and 70-gene signature are used to predict the risk of recurrence and benefit from chemotherapy. Methods: Discovery cohort (cohort 1) included 302 patients diagnosed with primary ER+/HER2- BC (1997-2005) in Stockholm health care region. Gene expression profiling has been performed using DNA microarrays (GSE48091) while information regarding tumor characteristics, treatment and follow-up have been obtained. TCGA’s dataset including 590 ER+/HER2- patients, was used as validation cohort (cohort 2). Kaplan–Meier estimates and Cox regression univariate/multivariable analyses were performed using breast cancer-specific survival(BCSS) and progression-free interval (PFI) as endpoints in cohorts 1 and 2, respectively. Gene signature scores were calculated using the R genefu package. Likelihood ratio (LR) tests and concordance indices (c-indices) were used to assess each score’s added prognostic value. Results: PD-L1 mRNA expression (treated as a continuous variable) was independently associated with better BCSS in cohort 1 (HR = 0.72; 95% CI = 0.58-0.90;p = 0.003) and with better PFI in cohort 2 (HR = 0.67; 95% CI = 0.50-0.90; p = 0.008) in the multivariable analysis. PD-L1 provided significant additional prognostic information beyond that of both RS alone (LR-Δχ2= 9.6; p = 0.002 and LR-Δχ2= 9.7; p = 0.002, in cohorts 1 and 2, respectively), and 70-gene signature score alone (LR-Δχ2= 10.4; p = 0.001 and LR-Δχ2= 9.2; p = 0.002 in cohort 1 and 2, respectively). C-indices for PD-L1 + RS vs RS were 0.65 vs 0.60 (cohort 1) and 0.66 vs 0.60 (cohort 2), and for PD-L1 + 70-gene vs 70-gene were 0.65 vs 0.59 (cohort 1) and 0.64 vs 0.54 (cohort 2), respectively. Conclusions: PD-L1 gene expression was correlated with better outcomes and can provide added prognostic value to RS and 70-gene signature scores in ER+/HER2- BC.