Malignant prolactinoma: case report and review of the literature.

Pituitary carcinomas are extremely rare. In general, the initial clinical, biochemical, and histological characteristics are of minimal utility in distinguishing benign adenomas from pituitary carcinomas. We describe a 63-year-old woman with a macroprolactinoma, who presented with diplopia and blurred vision. This unusual initial presentation and the subsequent aggressive clinical course, with diffuse local and distant intramedullary metastases, prompted us in retrospect to make a detailed analysis of the therapeutic interventions and histology. In addition, we reviewed all available literature on published cases of malignant prolactinoma and detailed their epidemiological, clinical, and histopathological characteristics. In brief, it is postulated that pituitary carcinomas arise from the transformation of initially large, but benign, adenomas. Unusual and/or atypical clinical manifestations appear to occur more frequently. In vivo, the development of dopamine agonist resistance in invasive macroprolactinoma is indicative of malignancy and should prompt the clinician to perform a biopsy of the tumor. For pituitary tumors that exhibit high mitotic activity, increased Ki-67 and/or p53 immunoreactivity, it may be useful to denote these tumors as 'atypical' prolactinomas to raise the possibility of future malignant development.