Anaplastic Carcinoma of the Pancreas Arising from Mucinous Cystic Neoplasm: A Case Report

Mucinous cystic neoplasm (MCN) is a pancreatic cystic lesion with a generally favorable prognosis; however, malignant transformation can occur. Anaplastic carcinoma of the pancreas is a rare and highly aggressive subtype of pancreatic cancer. Anaplastic transformation arising from MCN is extremely rare, and its clinicopathological features remain unclear. Herein, we report a case in which surgical resection was performed following systemic chemotherapy, highlighting a discrepancy between tumor marker levels and tumor progression.

A woman in her 40s presented with abdominal pain. CT revealed a 14-cm multilocular cystic lesion with a solid component in the pancreatic body and tail, accompanied by peritoneal nodules. The tumor marker carbohydrate antigen 19-9 (CA19-9) level was elevated (2100.0 U/mL). The clinical diagnosis was MCN with an associated invasive carcinoma and suspected peritoneal dissemination, and systemic chemotherapy was initiated. Following treatment, the solid component showed progressive enlargement, whereas the CA19-9 level decreased to 33.6 U/mL, and the peritoneal nodules regressed. The tumor subsequently perforated the colon and was complicated by intratumoral infection, requiring percutaneous drainage and laparoscopic ileostomy. Laparoscopic exploration revealed no obvious peritoneal dissemination, and ascitic fluid cytology was negative for malignancy (CY0). Therefore, distal pancreatectomy with partial gastrectomy and partial colectomy was performed. The resected specimen showed a 19-cm solid tumor with scattered multilocular cystic areas. Histopathology revealed highly atypical spindle, pleomorphic, and multinucleated tumor cells in the solid component, while the cystic component was lined by mucinous epithelium exhibiting carcinomatous atypia and associated ovarian-type stroma. The final pathological diagnosis was MCN with an associated invasive carcinoma with pleomorphic-type anaplastic carcinoma. Despite adjuvant chemotherapy, peritoneal recurrence occurred 3 months after surgery, and the patient died 5 months postoperatively.

Anaplastic carcinoma arising from MCN is extremely rare and exhibits aggressive clinical behavior with a poor prognosis, even after surgical resection. Tumor markers may not accurately reflect disease activity and should be interpreted with caution.