SUN-135 Characterization of Transcription Factor Immunostaining and Null Cell Adenoma Status in Hormone Negative Pituitary Adenomas

Introduction: Since the 2017 W.H.O. classification of pituitary adenomas redefined null cell adenomas (NCAs) as negative for all adenohypophyseal hormones and the transcription factors (TFs) SF-1, PIT-1, and T-PIT, limited data exist characterizing these tumors1. We characterize NCAs in comparison to hormone negative adenomas (HNAs), which demonstrate negative hormone immunostaining in the context of positive TF immunoreactivity. Methods: Retrospective review of 22 patients with HNAs between 2011-2019. Samples were stained for PIT-1 and SF-1. Negative ACTH staining served as a proxy for T-PIT given demonstrated prior concordance of these stains2. Demographics, tumor characteristics, preoperative symptoms, and postoperative outcomes were assessed. Results: Fifteen samples (68%) stained negative for both PIT-1 and SF-1 and were classified as NCAs. Seven were positive for SF-1 (n=3), PIT-1 (n=3), or both (n=1) and were classified as HNAs. NCA patients were predominantly female (80%), while those with HNAs were predominantly male (57%). All tumors were macroadenomas, with mean maximal tumor diameter of 28mm in NCAs vs 23mm in HNAs (p=0.2705). NCAs were more likely to demonstrate suprasellar invasion (100% vs. 71%, p=0.0325), and although not statistically significant, cavernous sinus invasion (53% vs. 43%, p=0.6695), and higher MIB-1 proliferative index (2.271 vs. 1.971, p=0.733). The most common preoperative symptoms were headache (73% NCA, 71% HNA) and vision loss (53%, 40%). Postoperative improvements in headache (60% NCA, 71% HNA) and vision (53%, 50%) were comparable. Sixty-four percent of NCAs underwent gross total resection vs. 43% of HNAs (p=.3712). There were no recurrences or progressions in either group over 24mo. Few comparisons reached significance, potentially due to limited sample size. Conclusion: A majority of HNAs demonstrated negative TF immunostaining and met criteria for NCAs. NCAs may be more common in females and demonstrate more suprasellar invasion than HNAs, but otherwise, do not vary significantly. TF staining may be of limited clinical utility in identifying high-risk pathology, however future studies with larger cohorts are warranted. References: 1. Osamura RY, Lopes MBS, Grossman A, Matsuno A, Korbonits M, Trouillas J, Kovacs K (2017) Pituitary adenoma. In: Lloyd RV, Osamura RY, Klöppel G, Rosai J (eds) World health organization classification of tumours of endocrine organs, 4th edn. IARC, Lyon, pp 14-18. 2. Nishioka H, Inoshita N