Pituitary Adenomas: MCM2 Protein as a Cell Proliferation Marker

Pituitary adenomas occasionally show aggressive behavior with rapid growth and invasion of the surrounding tissues. The identification of biological markers able to recognize aggressive pituitary adenomas in early stages remains a challenge. We aimed to determine the expression of a new cell proliferation marker with clinical significance in several human neoplasms, Mcm2, in pituitary adenomas and to establish the relationship of the Mcm2 index with tumor extension and invasion. The proliferative index was determined in tumor specimens of 64 patients with acromegaly or clinically nonfunctioning pituitary adenoma using immunohistochemical methods for two antigens, Mcm2 and Ki-67. Fifty-four (86%) adenomas showed immunoreactivity to Mcm2. The median Mcm2 index was 0.91% (range 0–13.24%). Immunoreactivity to Ki-67 was observed in 61 adenomas (95%). The median Ki-67 index was 0.88% (range 0–7.39%). A significant positive correlation was found between log Mcm2 index and log Ki-67 index (p < 0.001). Mcm2 and Ki-67 detected a similar number of proliferating cells. Mcm2 index showed a significant association with tumor extension (p = 0.02), but not with tumor invasion and hormone phenotype. In conclusion, we demonstrated that Mcm2 was similar to Ki-67 in the identification of the proliferating cells in this sample.