MIB-1 labeling index correlated with magnetic resonance imaging detected tumor volume doubling time in pituitary adenoma

Objective: The purpose of this study was to evaluate whether MIB-1 labeling index (LI) could be used to predict growth velocity of residual pituitary adenomas after surgery. Materials and methods: One hundred and sixty pituitary adenomas which had not received other treatment modality except for surgery were collected. Each of them had at least two post-operative magnetic resonance imaging (MRI) studies with an interval of at least 1 month apart. Tumor volume doubling time (TVDT) was calculated for those in which volume increased. Results: Post-operative tumor progression was noted in 54 (33.8%) cases, of which 39 (72.2%) cases were non-functioning adenomas. The MIB-1 LIs of the functioning and non-functioning adenomas were not significantly different. The median TVDT of these 54 cases was 34.6 months. The mean and median MIB-1 LI were 2.7 and 1.1 respectively (range 0.4-20.6). The MIB-1 LI was significantly correlated with log(2)(TVDT) (r=-0.363, P=0.007); when LI was < 0.8, the TVDT of 90.5% cases was >= 2 years. Conclusions: Only one-third of the pituitary adenomas progressed after surgery, and their MIB-1 LIs were generally low. The MIB-1 LI was significantly correlated with the MRI detected TVDT of post-operative residual pituitary adenomas.