A case of pulmonary adenocarcinoma showing rapid progression of peritoneal dissemination after immune checkpoint inhibitor therapy

Background Immune checkpoint inhibitors are standard treatments for non-small cell lung cancer. Unique cases with paradoxical acceleration of the disease after immunotherapy have been reported. These have been described as cases of hyperprogressive disease. Case presentation A 76-year-old man was diagnosed with pulmonary adenocarcinoma with pleural dissemination and liver and adrenal metastases. Genomic analysis revealed neither EGFR mutations nor ALK translocations. Immunohistochemical analysis revealed a programmed death-ligand 1 tumor proportion score of 23%. Chemotherapy with carboplatin, paclitaxel, and bevacizumab resulted in Grade 3 skin eruption and disease progression. Pembrolizumab was initiated as a second-line treatment. However, peritoneal dissemination and ascites developed. The patient died 2 weeks later. The autopsy revealed widespread peritoneal dissemination and an extensive hemorrhagic infarction. Conclusion This was a rare case of hyperprogressive disease with rapid progression of peritoneal dissemination after pembrolizumab treatment.