A Long-term Response to Nivolumab in a Case of PD-L1-negative Lung Adenocarcinoma with an EGFR Mutation and Surrounding PD-L1-positive Tumor-associated Macrophages

Anti-programmed cell death 1 (PD-1) antibodies have poor efficacy in epidermal growth factor receptor (EGFR)-mutated lung cancer. We herein report a 72-year-old man with programmed cell death-ligand 1 (PD-L1)-negative lung adenocarcinoma harboring an EGFR mutation that responded to nivolumab for more than 2 years. A pathological examination revealed infiltration of CD8-positive lymphocytes and macrophages expressing CD68, CD206, and PD-L1 into the PD-L1-negative tumor; CD206 expression is a marker of immunosuppressive tumor-associated macrophages (TAMs). The presence of PD-L1-positive TAMs in the tumor environment might be a predictor of a positive response to anti-PD-1 antibodies.