Inherent PD-L1 22C3 Expression in Alveolar Macrophages Impacts the Combined Positive Score Status in Breast Cancer With Pulmonary Metastasis.

Objective: This study aimed to determine the impact of inherent programmed death-ligand 1 (PD-L1)-expressing alveolar macrophages (AMs) on the combined positive score (CPS) of PD-L1 (22C3) in metastatic breast cancer in the lungs.

Methods: A total of 87 patients with pulmonary metastases of breast cancer were included in this study. Immunohistochemical staining of various PD-L1 antibodies was performed. The CPSs and CPSs excluding the number of PD-L1 positive AMs [CPS(NAM)s] with PD-L1 (22C3) were determined and compared.

Results: Among 87 enrolled patients, 22 had luminal A breast cancer, 24 had luminal B breast cancer, 13 had HER-2-positive breast cancer, and 28 had triple-negative breast cancer (TNBC). CPSs ≥ 10 was observed only in luminal B (12.5%) and TNBC (35.7%) subtypes (p < 0.001), whereas CPS(NAM)s ≥ 10 was observed only in TNBC (14.3%) (p = 0.011). Changes from the CPS-positive to the CPS(NAM)-negative status occurred in nine cases (10.3%), with significantly higher proportions being observed in the luminal B (12.5%) and TNBC (21.4%) subtypes (p = 0.007). Tumors showing changes from the CPS-positive to the CPS(NAM)-negative status were larger (p < 0.001); similar findings were observed in the TNBC subgroup (p = 0.001).

Conclusions: The inclusion of PD-L1 expressing AMs leads to differences in CPS positivity, especially in large TNBC subtype tumors.