P53 and MIB-1 Immunohistochemistry As Predictors of the Clinical Behavior of Nonfunctioning Pituitary Adenomas

Background: P53 expression and increased MIB-1 proliferation index have been shown to correlate with invasive behavior in pituitary adenomas. The purpose of this study was to determine whether these indices could be used to predict a higher likelihood of recurrence in clinically nonfunctional pituitary adenomas and thus guide adjuvant therapy.

Methods: Fifty-one clinically nonfunctional pituitary adenomas were selected from the database at the Vancouver Hospital and Health Sciences Center between the years 1990-1998. Included were 32 nonrecurrent and 19 recurrent adenomas.

Results: The mean initial labelling index for p53 in nonrecurrent tumours was 0.38% (0-1.58%), while it was 0.46% (0-3.65%) for recurrent adenomas. The mean initial MIB-1 index for nonrecurrent tumours was 1.63% (0.08-9.36%), while for recurrent tumours it was 1.92% (0-7.76%). The percentage of p53 positive adenomas was 66% for nonrecurrent tumours and 68% for recurrent tumours. None of the differences in the labelling indices between the recurrent and nonrecurrent groups was statistically significant. As 12 patients (38%) in the nonrecurrent group had undergone radiotherapy as initial adjuvant therapy after surgery and none of the recurrent group had done so, patients who did not receive radiotherapy in the nonrecurrent group were analyzed separately. Again, none of the differences in the labelling indices between the recurrent and nonrecurrent groups was statistically significant when the effect of radiotherapy was removed from the analysis.

Conclusions: The results demonstrate no statistical difference in the p53 or MIB-1 labelling indices between recurrent and nonrecurrent nonfunctional pituitary adenomas. Concern should be raised in attaching too much clinical significance to these labelling indices, especially with respect to p53 as a predictor of the clinical behavior of nonfunctional pituitary adenomas.