Mucinous cystic neoplasm (mucinous cystadenocarcinoma of low-grade malignant potential) of the pancreas - A clinicopathologic study of 130 cases

Mucinous cystic neoplasms (MCNs) of the pancreas are uncommon tumors. The c lassification and biologic potential of these neoplasms remain the subject of controversy. Attempts to classify these tumors in a similar manner to ov arian MCNs remains controversial, as even histologically benign-appearing p ancreatic MCNs metastasize and are lethal. One hundred thirty cases of MCNs were identified in the files of the Endocrine Pathology Tumor Registry of the Armed Forces Institute of Pathology from the years 1979 to 1993. The pa thologic features, including hematoxylin and eosin staining, histochemistry , immunohistochemistry (IHC), cell cycle analysis, and K-ras oncogene deter mination were reviewed. These findings were correlated with the clinical fo llow-up obtained in all cases. There were 130 women, aged 20-95 years (mean age at the outset, 44.6 years). The patients had vague abdominal pain, ful lness, or abdominal masses. More than 95% of the tumors were in the pancrea tic tail or body and were predominantly multilocular. The tumors ranged in size from 1.5 to 36 cm in greatest dimension, with the average tumor measur ing >10 cm. A spectrum of histomorphologic changes were present within the same case and from case to case. A single layer of bland-appearing, sialomu cin-producing columnar epithelium lining the cyst wall would abruptly chang e to a complex papillary architecture, with and without cytologic atypia, a nd with and without stromal invasion. Ovarian-type stroma was a characteris tic and requisite feature. Focal sclerotic hyalinization of the stroma was noted. This ovarian-type stroma reacted with vimentin, smooth muscle actin, progesterone, or estrogen receptors by MC analysis. There was no specific or unique epithelial IHC. K-ras mutations by sequence analysis were wild ty pe in all 52 cases tested. Ninety percent of patients were alive or had die d without evidence of disease (average follow-up 9.5 years), irrespective o f histologic appearance; 3.8% were alive with recurrent disease (average 10 years after diagnosis); and 6.2% died of disseminated disease (average 2.5 years from diagnosis). Irrespective of the histologic appearance of the ep ithelial component, with or without stromal invasion, pancreatic MCNs shoul d all be considered as mucinous cystadenocarcinomas of low-grade malignant potential. Pancreatic MCNs cannot be reliably or reproducibly separated int o benign, borderline, or malignant categories.