Carbohydrate antigen 19-9 expression by folliculo-tubular structures of normal and neoplastic pituitary

We demonstrated immunohistochemically that follicular lining cells of anterior pituitary display carbohydrate antigen 19-9 (CA19-9) at their luminal surfaces. CA 19-9 was also demonstrated in the tubular structures of the intermediate lobe. Until now this antigen of exocrine ducts, such as pancreatic and salivary ducts, has not been demonstrated in endocrine tissue. Some CA19-9 positive follicular cells also showed endocrine markers such as chromogranin, synaptophysin and pituitary hormones. In pituitary adenomas, frequently-seen follicular structures showed immunohistochemical features similar to non-neoplastic follicles. Expression of CA19-9 in the adenohypophysis may be related to its origin from an anlage, the stomodeum shared with the parotid gland. The lining cells and mucin of Rathke's cleft cysts also revealed CA19-9. Accordingly, these cysts could have arisen from follicular cells with an exocrine ductal phenotype. The transitional cell tumor of Kepes also showed CA19-9 at the luminal surfaces of cells and in the mucin of large cysts. Given that smaller mucin-laden cysts appeared fairly frequently in adenomas, the transitional cell tumor may be a kind of pituitary adenoma with follicles in which many cells produce excessive mucin.