Successful Conversion Surgery for Unresectable Microsatellite Instability-High Pancreatic Tail Cancer Following...

Pembrolizumab was approved for the treatment of microsatellite instability (MSI)-high pancreatic cancer that is unresponsive to systemic chemotherapy. However, pancreatic cancer has a low prevalence of MSI-high status (<1%). We report a rare case of MSI-high pancreatic tail cancer successfully treated with pembrolizumab, which enabled conversion surgery to be performed.

A 78-year-old male patient received the diagnosis of unresectable metastatic (UR-M) pancreatic tail cancer with para-aortic and anterior mediastinal lymph node metastases. Tests found high MSI due to the loss of MSH2 and MSH6 expression. Following 6 courses of pembrolizumab, he achieved a partial response. Pembrolizumab was discontinued after immune-related renal dysfunction developed during the 7th course. Fluorodeoxyglucose positron emission tomography/computed tomography demonstrated decreased uptake in the anterior mediastinal and para-aortic lymph nodes, allowing a radical resection to be performed. The patient underwent a radical antegrade modular pancreatosplenectomy with a left adrenalectomy and para-aortic lymph node sampling. Currently, at postoperative month 6, he is alive and recurrence-free. The present case is an extremely rare instance of MSI-high, unresectable pancreatic cancer that was removed by curative resection after pembrolizumab therapy.

The present rare case of conversion surgery for MSI-high UR-M pancreatic tail cancer, achieving a pathological partial response after pembrolizumab treatment, highlights the potential of pembrolizumab against this specific molecular subtype of pancreatic cancer and underscores the clinical significance of proactively testing for MSI to identify candidates for immunotherapy and curative conversion surgery.