Pituitary tumors are commonly encountered, benign adenomas that arise from cells of the anterior pituitary gland. These tumors arise from highly differentiated cells expressing unique hormone gene products, including growth hormone, prolactin, ACTH, TSH, FSH and LH. They may be functional and actively secrete hormones, leading to characteristic clinical features including acromegaly, Cushing's disease, features of hy-perprolactinemia or, rarely, hyperthyroidism. Commonly, they are nonfunctional, leading primarily to hypogonadism and compressive pituitary failure. These monoclonal neoplasms account for ~ 15% of all intracranial tumors, and malignant transformation very rarely occurs (Melmed 2003). The direct pathogenesis of these tumors remains elusive, and genetic, cellular, animal and human pathologic models have been developed to further understand pituitary tumor origins.
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