Is Ki-67 Index an Useful Labeling Marker for Invasion of Pituitary Adenomas?

The Ki-67 antigen is a protein expressed in cell nuclei throughout the entire cell cycle. It is related to the cell proliferation in a variety of pituitary tumors. Pituitary tumors are usually benign, but may be aggressive and invade surrounding tissues in about one third of the cases. The aim of this study is to determine the proliferative index of the pituitary adenomas, using MIB-1 monoclonal antibody in paraffin embedded sections and also to correlate this index with clinical parameters and radiological evidence of invasiveness. Twenty-eight patients (mean age, 46.46 +/- 13.14; range, 13-80 yr) who underwent surgery for pituitary adenomas were enrolled in this study. Immunohistochemical staining for anti-Ki-67 monoclonal antibody (MIB-1) was performed and the proliferative activity was determined as the percentage of MIB-1 labeled nuclei (MIB-1 index). The overall mean Ki-67 labeling index was 2.04 +/- 1.17 (range 1-5). This index was not associated with gender and age of the patients and functional status of pituitary adenomas. Although Ki-67 index was higher in suprasellar adenomas than in sellar adenomas, the difference was not statistically significant (2.20 +/- 1.15 for suprasellar adenomas vs. 1.85 +/- 1.21 for sellar adenomas; p=0.316). Ki-67 index was distributed almost the same amount between the groups of adenomas with (2 +/- 1.51) or without cavernous sinus invasion (2.05 +/- 1.03) (p=0.498). Unexpectedly, no significant relationship was identified between proliferation index and the invasiveness of pituitary adenomas in this study, but this raises the question whether proliferation markers in pituitary adenomas are useful or not?