Progressive Estrogen Receptor Acquisition During Malignant Transformation: Insights From MCN‐Derived Anaplastic Pancreatic Carcinoma

Anaplastic pancreatic carcinoma (APC) arising from mucinous cystic neoplasm (MCN) is rare, with only 12 cases reported. The relationship between pregnancy-associaed hormonal changes and MCN progression remains poorly understood, particularly regarding hormone receptor expression patterns during malignant transformation. A 34-year-old woman presented with persistent abdominal pain 9 months post-delivery. Imaging revealed an 11 cm multilocular cystic mass in the pancreatic body and tail with mural nodules showing blood flow signals. Laboratory findings demonstrated normal. She underwent distal pancreatectomy and splenectomy and no recurrence at 6-month follow-up. Histopathological examination revealed MCN with ovarian-type stroma progressing from low-to-high grade dysplasia, invasive ductal carcinoma, and anaplastic carcinoma with osteoclast-like giant cells. Immunohistochemically, estrogen receptor (ER) expression showed stepwise pattern: negative in low-grade dysplasia, strongly positive in high-grade dysplasia and anaplastic components. Progesterone receptor positivity was observed in stromal and epithelial components, with elevated Ki-67 correlating with ER expression. This represents first documentation of progressive ER acquisition during MCN malignant transformation, suggesting autonomous hormone production by ovarian‑type stroma may help sustain tumor growth beyond pregnancy. Stepwise ER expression may serve as a biomarker for risk stratification and a potential target for therapy in hormone-sensitive pancreatic neoplasms.