PD-L1 Expression of Lung Cancer Cells,Unlike Infiltrating Immune Cells,Is Stable and Unaffected by Therapy During Brain Metastasis

BackgroundApproximately 50% of brain metastases originate from non–small-cell lung cancer. The median survival of patients with brain metastases is 1 month without treatment. Novel immunotherapeutic strategies, such as those targeting the programmed death ligand 1 (PD-L1)/programmed cell death 1 (PD-1) axis, are promising in patients with advanced systemic disease but are often preferentially administered to patients with tumors showing PD-L1 positivity.Patients and MethodsSurgically resected paired primary lung adenocarcinoma and brain metastasis samples of 61 patients were analyzed. We compared the paired samples regarding the amount of peritumoral and stromal mononuclear infiltration, PD-L1 expression of tumor and immune cells, and PD-1 expression of immune cells. We investigated the effect of radiotherapy, chemotherapy, and steroid therapy on PD-L1 expression in brain metastases.ResultsThere was significant positive correlation regarding the PD-L1 expression of tumor cells between the paired primary lung adenocarcinoma and brain metastatic samples with the use of different cutoff levels (1%, 5%, 50%). We found no impact of chemotherapy or steroid therapy on the changes of PD-L1 expression of tumor cells between the 2 sites. There is no or only limited concordance of the proportion of PD-1– or PD-L1–positive tumor-associated immune cells between the paired tumor samples, which suggests that brain metastases develop their own immune environment.ConclusionWe observed a strong correlation of PD-L1 positive tumor cells between primary lung adenocarcinoma cases and their corresponding brain metastases, which is not significantly influenced by chemotherapy or steroid therapy.