Background: The status of tumor-infiltrating lymphocytes (TILs) is a prognostic factor for triple negative breast cancer (TNBC). Recent studies have shown that programmed cell death 1 (PD-1) or programmed death ligand 1 (PD-L1) is expressed on T lymphocytes or tumor cells modulating antitumor immunity. The regulation of immune checkpoints between tumor cells and T lymphocytes may serve as a target for improvement of TNBC prognosis. We investigated TILs and PD-L1 status in TNBCs before or after preoperative systemic therapy (PST) to elucidate the clinical significance of PD-L1 expression.
Methods: Ninety patients received PST, and materials of core needle biopsies (CNB) taken before PST were available for 32 patients. TILs were scored as "% stromal", and tumors were defined as High-TILs (≥30%) or Low-TILs (<30%). The expression of PD-L1 was assessed by immunohistochemistry.
Results: TILs status in CNB is significant in pathological therapeutic grade: 1 vs. 2 or 3 (p = 0.0359). Disease-free survival (DFS) in patients with Low-TIL tumors were significantly worse than those with High-TIL tumors (p = 0.0383), but overall survival (OS) showed no significance (p = 0.0772). However, in patients with Low-TIL tumors, both DFS and OS in patients with High-PD-L1 expression were extremely unfavorable than in patients with Low-PD-L1 expression (p = 0.0032, p = 0.0002).
Conclusion: The patients with TNBCs with combined Low-TILs and High-PD-L1 status in pre-PST situation showed unfavorable prognosis. The subset of TNBCs with Low-TILs and High-PD-L1 status could be the therapeutic target for immune checkpoint inhibitor.
Keywords: Immune checkpoints; PD-L1; TILs; TNBC; Tumor-infiltrating lymphocytes.