Evaluation of tumor-infiltrating lymphocytes, PD-L1, and mutations and association with prognosis in HER2-positive early stage breast cancer.

Background: Tumor-infiltrating lymphocytes (TILs) have predictive and prognostic potential in HER2-positive breast cancer (HER2+ BC). Programmed death-ligand 1 (PD-L1) is an immune checkpoint protein, with important roles in the tumor microenvironment, possibly in both tumor and immune cells (ICs), providing rationale for targeting with immune-checkpoint therapy. mutations are oncogenic, activating mutations, which are also of relevance in breast cancer. Herein, we investigate the frequency of TILs, PD-L1 and mutations, and whether these factors influence outcome, in early HER2+ BC.

Materials And Methods: Stromal TILs (sTILs) and PD-L1 expressions were assessed using full tumor-sections and TMA, respectively, from 236 patients with HER2+ BC. TILs were assessed, according to a standardized method, as continuous measurement and according to three predefined categories: low (0-10%), intermediate (11-59%), and high (60-100%). PD-L1 immunohistochemistry (Ventana SP263) was evaluated and positivity defined as ≥1% expression in tumor and ICs. mutations (exons 9 and 20) were determined by pyrosequencing.

Results: Fourteen percent of patients had high sTILs and 25% had a mutation. PD-L1 expression was more frequent in ICs (68%) than tumor cells (24%). Patients with low sTILs had a significantly worse overall survival (multivariate: HR 2.80; 95% CI 1.36-5.78;  = .02).

Discussion: Patients with low sTILs had a significantly poorer survival, despite adequate treatment with adjuvant therapy.