Rapid intracystic growth of spindle cell-type anaplastic carcinoma derived from intraductal papillary mucinous carcinoma.

Anaplastic carcinoma of the pancreas (ACP) is a rare and aggressive malignancy. We report a case of spindle cell-type ACP arising from intraductal papillary mucinous carcinoma (IPMC) showing rapid intra-cystic growth. A 73 year-old man was incidentally found to have a pancreatic cyst, initially diagnosed as a simple cyst. After 18 months, a solid component appeared within the cyst and rapidly enlarged within one month. Distal pancreatectomy was performed. Histopathology revealed spindle cell-type anaplastic carcinoma arising from invasive IPMC. Despite aggressive histology, curative resection was achieved. The patient remains recurrence-free for 50 months. Rapid changes in pancreatic cysts warrant careful evaluation and timely surgical intervention.