Aggressive pituitary tumors.

Although almost all pituitary tumors are benign adenomas, a surprisingly large number of these tumors invade tissues outside of the pituitary gland. Such invasion, by itself, is not diagnostic of pituitary carcinomas, which are exceedingly rare (0.13% of 2,342 pituitary tumors in one series). Several different criteria are available to determine whether a tumor is invasive. Intraoperative biopsies demonstrate an 85% incidence of microscopic invasion of the dura. Evidence of gross invasion at surgery and radiologic evidence of invasion on magnetic resonance imaging (MRI) and computed tomographic (CT) scans occur at a much lower incidence but may be more predictive of surgical cure. Invasive adenomas also have higher proliferation rates than do noninvasive adenomas, as shown by immunohistochemical detection of proliferating cell nuclear antigen (PCNA), Ki-67, and MIB-1. The expression of p53, increased epidermal growth factor receptors, and protein kinase C activity also correlate with invasion and aggressive behavior. Clinically significant invasion is more frequent with macroadenomas. Macroadenomas of all pituitary tumor subtypes except gonadotroph macroadenomas have a greater than 50% incidence of gross invasion. Currently, there is no accepted means of predicting an adenoma's clinically significant invasiveness and long-term aggressiveness.