Endocrine Abstracts

Introduction: Pituitary adenomas (PA) represent approximately 15% of all intracranial neoplasms, with a global incidence of 15,20 per million per year. The immunohistochemical analysis of PA is necessary for diagnosis and plays an important role in the modern classification system of pituitary tumors.

Material and methods: Samples from 142 surgically resected PA were studied immunohistochemically using antisera for 6 anterior pituitary hormones. Reticulin fiber staining and routine hematoxylin-eosin staining were also used. There were 57 patients with acromegaly (ACM), 29 prolactinomas (PRM), 55 non-functioning PA (NFPA) and 1 PA with mixed secretion of growth-hormone (GH) and prolactin (PRL).

Results: Immunohistochemical staining was positive for one hormone in 44% cases, 34% staining positive for multiple hormones. 21% of tumors failed to stain for any of the main pituitary hormones (null-cell adenomas). Most PA were acidophilic (105/142), the rest being basophilic (14/142), chromophobe (7/142) or mixed (16/142). In patients with ACM, most tumors were GH- (54%), mixed GH and PRL-producing (23%) and plurihormonal PA (9%). In the other cases (14%) the immunostaining results were discordant with the clinicobiological data. Prolactinomas were 75% PRL-producing PA, the rest being mixed GH and PRL or plurihormonal (7% each); discordant results were obtained in 11%. In our study, 32/55 (58%) of NFPA showed hormonal immunoreactivity: 13.5% (5/37) for GH, 89% (16/18) for FSH/LH, 6/13 (46%) plurihormonal PA and 11% (2/18) mixed GH-PRL. TSH, PRL and ACTH exclusive immunoreactivity were found each in one case. Most tumors immunopositive for GH (28/37), GH and PRL (13/18) and plurihormonal (8/13) were positive for reticulin, while those positive for PRL (9/23), ACTH (1/2), FSH-LH (7/18) and null-cell adenomas (14/30) stained less for reticulin. The only TSH-producing adenoma in the study stained negative for reticulin.

Conclusion: The immunohistochemical characterization of PA is useful for an accurate diagnosis. However, the hormonal immunoreactivity of these tumors is not always correlated with the synthesis and the release rate of the hormones. That is why the revised classification of pituitary adenomas (WHO, 2017) recognizes the role of many other immunohistochemical markers and transcription factors. Their widespread use will hopefully aid in the early identification of aggressive pituitary adenomas and in improving management strategies.