Case 2. A 63-year-old man with a smoking history of 43 pack-years was referred to our hospital for a detailed examination of abnormal shadows on chest radiography. Chest CT revealed an irregular nodule (15 mm) in the right upper pulmonary lobe with lymphangitic carcinomatosis and multiple enlarged right hilar and mediastinal lymph nodes. EBUS-TBNA was performed for the sub-tracheal lymph nodes, and immunohistochemistry confirmed lung adenocarcinoma. Biomarker tests were negative for both EGFR mutation and ALK translocation, and PD-L1 was highly expressed (TPS: 70%). The clinical stage after a systemic evaluation was cT3N3M1c (LYM), stage IVB with cervical lymph node metastasis. Pembrolizumab monotherapy was initiated. PR was observed after two cycles, and CR was achieved after 12 cycles. After completion of 34 cycles of pembrolizumab (the patient skipped one cycle for his own convenience), the patient was found to have maintained CR during treatment-free follow-up and is currently alive 42 months after the start of treatment.