Durable Response to PD-1 Blockade in a Patient With Metastatic Pancreatic Undifferentiated Carcinoma With Osteoclast-Like Giant Cells.

Undifferentiated carcinoma with osteoclast-like giant cells (UCOGC) of the pancreas is a rare and potentially aggressive variant of pancreatic ductal adenocarcinoma. Data on this disease are sparse, and despite genetic similarities to pancreatic ductal adenocarcinoma, UCOGC clinical outcomes can be markedly different. We report on a female patient aged 62 years who presented with UCOGC with pulmonary metastases initially treated with 2 lines of cytotoxic chemotherapy. After rapid disease progression with both cytotoxic treatments, the patient's tissue was sent for next-generation sequencing, which revealed a high tumor mutation burden (32 mutations per megabase), as well as somatic mutations in BRAF, NF1, PIK3CA, CDKN2A, TERT, and TP53. Pancreatic cancers have previously demonstrated suboptimal responses to immunotherapeutic approaches. However, given the high tumor mutation burden and distinctiveness of the tumor class, the patient began third-line pembrolizumab monotherapy after palliative radiation to the rapidly progressing and painful abdominal mass from her primary tumor. She had a marked response in her primary UCOGC tumor and metastatic sites, and she remains on pembrolizumab monotherapy with ongoing response after 32 months of therapy. Recent evidence showing significant PD-L1 enrichment on neoplastic cells of undifferentiated carcinomas (including UCOGC) may indicate a role for immunotherapeutic approaches in these patients. Rare cancers such as UCOGC and other undifferentiated carcinomas may benefit from next-generation sequencing to inform treatment decisions when standards of care are absent, as in this report.