Intracranial Response to Nivolumab in a Patient with PD-L1-negative Lung Adenocarcinoma

We herein report the case of a 52-year-old man with stage IV lung adenocarcinoma. The patient was negative for epidermal growth factor receptor (EGFR) mutations and echinoderm microtubule-associated protein-like 4 (EML4) /anaplastic lymphoma kinase (ALK) rearrangement. He was treated with nivolumab as a third-line chemotherapy. After four cycles of nivolumab treatment, a partial response was observed in the brain and at the primary tumor site. Nivolumab treatment has been continued for 11 months without progression. Immunohistochemistry revealed that the programmed death-ligand 1 (PD-L1) expression was 0% (according to the tumor proportion score). Our case indicates that the efficacy of programmed cell death 1 inhibitors is not solely predicted by the PD-L1 status, and that immune checkpoint inhibitors might be effective for the treatment of central nervous system metastasis.