A rare adenocarcinoma with poor prognosis, arising from the adenohypophysial cells of the anterior lobe of the pituitary gland or pre-existing adenomas. The majority are hormonally functioning neoplasms, usually producing prolactin or ACTH. The diagnosis is based on the presence of metastases. Syndromes associated with pituitary gland carcinomas include hyperprolactinemia, Cushing disease, and acromegaly.