A case of MSI-high pancreatic body-tail cancer successfully treated with radical resection after pembrolizumab.

A 72-year-old woman was diagnosed with unresectable pancreatic body-tail cancer (cT4N1M1, cStage IV) with para-aortic lymph node metastasis. She underwent six courses of gemcitabine + nab-paclitaxel as first-line chemotherapy, 12 courses of oxaliplatin + irinotecan + levofolinate + fluorouracil as second-line chemotherapy, and five courses of albumin-suspended irinotecan + levofolinate + fluorouracil as third-line chemotherapy. After each chemotherapy regimen, the disease was determined to be progressive. Analyses of endoscopic ultrasound-fine needle aspiration specimens and peripheral blood samples revealed microsatellite-instability (MSI)-high pancreatic cancer. The patient underwent 19 courses of pembrolizumab and achieved a partial response. She then underwent conversion surgery, including distal pancreatectomy, lymph node dissection, local gastrectomy and partial mesenteric resection of transverse colon. She is currently alive without recurrence at 18 months postoperatively. It is extremely rare for patients with unresectable and MSI-high pancreatic cancer to successfully undergo conversion surgery after pembrolizumab treatment.