Outcome of patients with metastatic triple negative breast cancer treated with first-line chemotherapy: a single institution retrospective analysis

Purpose: Metastatic triple negative breast cancer (mTNBC) is associated with poor prognosis and limited treatment options. It is known to be high immunogenic, with a high level of programmed cell death-ligand 1 (PD-L1) expression. PD-L1 expression in TNBC does not have a clear prognostic relevance. In this study, we aimed to assess survival outcomes according to PD-L1 expression in the real world. Methods: We retrospectively analyzed mTNBC patients treated with first-line chemotherapy at European Institute of Oncology with evaluable PD-L1 expression. Primary endpoints were Progression-Free Survival (PFS) and Overall Survival (OS) according to PD-L1 expression. Results: From January 2000 to December 2018, 190 patients fulfilled the inclusion criteria for final analysis. PD-L1 positive (≥ 1%) subgroup showed a median PFS of 6.8 vs 5.6 months in PD-L1 negative subgroup (PFS-HR 1.25, 95% CI 0.89–1.74, p-value = 0.191), while at data cutoff we had 120 deaths in the PD-L1 < 1% population with a median OS of 22.1 months and 42 deaths in PD-L1 positive patients with a median OS of 20.8 months (OS-HR 1.09, 95% CI 0.76–1.55, p-value = 0.64). No difference in PFS and OS was related to the choice of chemotherapy (p-value for PFS: 0.19, p-value for OS: 0.53). Conclusion: No differences in clinical outcome were found according to PD-L1 status or chemotherapy regimen chosen. In “unselected” patients, single agent or combination chemotherapy could be appropriate, although in the immunotherapy era patients with newly diagnosed mTNBC should be routinely tested for PD-L1 status. The variability in PD-L1 expression by metastatic site warrants further investigation.