Pancreatic undifferentiated carcinoma with osteoclast-like giant cells curatively resected after pembrolizumab therapy for lung metastases: a case report

BACKGROUND: Therapy targeting programmed death-1 or programmed death-1 ligand-1 (PD-1/PD-L1) has been developed for various solid malignant tumors, such as melanoma and non-small-cell lung cancer (NSCLC), but this approach has little effect in the treatment of pancreatic cancer. Pancreatic undifferentiated carcinoma with osteoclast-like giant cells (UCOGC) is a rare pancreatic malignancy having unique morphology and is considered a variant of pancreatic ductal adenocarcinoma (PDAC). Although UCOGC has been reported to have better prognosis than conventional PDAC, the optimal treatment for UCOGC with distant metastases has not been determined. CASE PRESENTATION: A 66-year-old man was initially diagnosed with NSCLC with multiple intrapulmonary metastases and abdominal lymph node metastasis in the tail of the pancreas, and bronchial biopsy and diagnostic imaging were performed. Pathologic examination of the lung showed poorly differentiated adenocarcinoma cells expressing epithelial marker and PD-L1. Therefore, pembrolizumab monotherapy for NSCLC was given. The pulmonary lesions shrank markedly and were in complete remission after 8 months of anti-PD-1 therapy, though no therapeutic effect was observed in the pancreatic site. Distal pancreatectomy was then performed, and histopathological examination showed that the tumor was UCOGC originating from the pancreas. The histologic findings of the resected specimen mimicked those of the lung biopsy specimen, leading to the final assessment that the lung tumors were metastatic foci that migrated from the UCOGC, and only the metastatic lesions benefited from pembrolizumab therapy. CONCLUSION: Immune checkpoint inhibitors have limited therapeutic effects on primary lesions of pancreatic cancer, but they may exert antitumor effects on pulmonary metastases of UCOGC.