Abstract
BACKGROUND Mucinous cystic neoplasm (MCN) of the pancreas is a rare mucin-producing cystic neoplasm that has a characteristic histological feature referred to as ovarian-type stroma (OS) underlying the epithelium. Pancreatic ductal carcinoma arises from MCN as a precursor lesion, but data on progression pathways are limited. CASE REPORT A 40-year-old female was referred to our hospital for further investigation of a pancreatic cyst. Further examination showed a 7.0 cm multilocular cyst in the pancreatic tail and a solid mass in the thick septum of the cystic tumor. Distal pancreatectomy and splenectomy were performed. Histological examination revealed a moderately differentiated invasive ductal carcinoma (IDC) with a diameter of 0.5 cm in the thick septum of the cystic lesion and a cyst wall composed of epithelium with low-grade to severe dysplasia. The epithelium covered an OS. Pathological diagnosis was IDC arising in MCN of the pancreas. Immunohistochemical examination showed that MUC1 expression was negative in MCN but positive in IDC. KRAS mutation was observed in both MCN and IDC regions. CONCLUSIONS We present a rare case of moderately differentiated pancreatic IDC arising in MCN. To elucidate the underlying progression pathway, we explored the correlation between KRAS mutation and MUC expression as a clinicopathological parameter.