Clinical Features and Growth Fractions of Pituitary Adenomas

Background: The Ki-67 monoclonal antibody is expressed by proliferating and dividing cells, but not by resting cells. The specificity of the monoclonal antibody, MIB-1, against the Ki-67 antigen has been established by immunostaining of formalin-fixed paraffin-embedded tissue in a microwave oven.

Methods: The growth fraction of 85 pituitary adenomas was studied retrospectively by immunohistochemical analysis using the monoclonal antibody MIB-1. The adenomas were classified into three types: microadenoma, expansive type, and invasive type, based on findings on Gd DTPA enhanced magnetic resonance imaging.

Results: The mean MIB-1 index in nonfunctioning microadenomas was higher than in expansive and invasive adenomas, but this difference was not significant. The MIB-1 index in younger patients (under 30 years) with nonfunctioning adenomas was significantly higher than in patients over 40 years of age. One of 14 patients with recurrent disease had an elevated MIB-1 index, but generally patients with an MIB-1 index over 2.0% did not suffer recurrence. The mean MIB-1 index was higher in expansive and invasive functioning adenomas than microadenomas, but not significantly. No correlation between the MIB-1 index and the serum GH or PRL concentration was established. No MIB-1 positive nuclei were observed in two GH-producing adenomas treated with the somatostatin analog SMS 201-995.

Conclusions: No significant relationship was identified between growth fraction and the invasiveness or recurrence of pituitary adenomas. The growth fraction of nonfunctioning pituitary adenomas was higher in patients under 30 years than over 40 years of age.