We report a case of late-onset hyperprogressive disease after cessation of a PD-1 inhibitor. A male was diagnosed with metastatic lung adenocarcinoma with little progression for 2 months before treatment. He received pembrolizumab as a second-line treatment and was subsequently prescribed docetaxel for 3 months until a slight increase in pleural effusion. At the time of progression to docetaxel, he commenced prednisolone because of immune-system-related diarrhea. After that, his general condition rapidly worsened with severe fatigue and hypoxia. Computed tomography revealed a massive increase of pleural effusion and replacement of almost the entire liver with cancer over a period of 5 weeks.