Pituitary Adenoma: A Pathologic Classification of Tumors

The classification of pituitary adenomas now includes an “atypical” variant, which can be defined as MIB-1 proliferative index greater than 3%, excessive p53 immunoreactivity, invasive growth pattern, and the increased mitotic activity. Recent guidelines do not precisely define the cutoff points for elevated mitotic activity. Therefore, this study was designed to obtain reliable cut-off values for the mitotic index.

In this study, the authors reviewed the records belonged to 300 patients including 250 patients with typical pituitary adenoma and 50 patients with atypical pituitary who were referred to Loghman Hakim Hospital between 2011 and 2017. Statistical analyses were performed using Fisher’s exact test and Mann Whitney. Also, Cut-off values were attained using ROC analysis.

In APAs group, 47.8% and 52.2% of the tumors were microadenomas and macroadenomas, respectively. 91.3% of the patients with APAs had Ki-67 labeling index more than 3%, and the presence of p53 protein was observed in all the patients with APAs. The mean number of mitosis in the TPAs and APAs groups was 0.62 and 2.5, respectively. In addition, our results showed significant threshold values for mitotic index (>2 mitosis within 10 high power fields). Also, there was no significant difference between the size of tumors and type of secretion hormones in the APA and TPA groups (P> 0.05).

We introduced a new cut-off for the mitosis index (greater than 2) that may help to more reliable diagnosis of atypical adenomas (APA). These findings will convince pathologists to adopt this clinicopathological classification, and those clinicians will consider it as helpful when choosing the appropriate therapeutic strategy.