SUN-080 - Primary Papillary Epithelial Tumor of the Sella: A Diagnostic Challenge Among TTF-1 Positive Sellar Lesions

Introduction:
Primary Papillary Epithelial Tumor of the Sella (PPETS) is a rare, non-adenomatous epithelial neoplasm involving the sellar and suprasellar region. First described in 2020, its clinical, radiological, and immunohistochemical features frequently mimic pituitary adenomas or metastatic carcinomas, particularly of pulmonary or thyroid origin, representing a major diagnostic pitfall. In tertiary centers, papillary epithelial tumors account for less than 0.1% of sellar masses and are likely underdiagnosed due to the lack of standardized diagnostic criteria.

Case Report:
A 28-year-old woman presented with a two-year history of amenorrhea and progressive visual blurring. Endocrine evaluation revealed central hypothyroidism. Brain MRI demonstrated a sellar mass with suprasellar extension and cavernous sinus involvement, measuring 3.5 × 2.8 × 3.2 cm, with lobulated contours, “snowman” configuration, isointensity on T1-weighted images, hyperintensity on T2/FLAIR, and heterogeneous internal signal. The initial radiological diagnosis was pituitary macroadenoma.
The patient underwent transsphenoidal resection and developed secondary adrenal insufficiency, arginine vasopressin deficiency, and persistent amenorrhea, requiring hormone replacement therapy. Initial histopathological analysis suggested metastatic adenocarcinoma of probable pulmonary origin, with immunopositivity for AE1/AE3, CAM5.2, and TTF-1, and a Ki-67 index of approximately 30%. Thoracic investigation failed to identify a primary tumor, prompting pathological review. Reevaluation demonstrated a solid-papillary neoplasm composed of rounded epithelial cells without significant atypia, arranged in solid nests and papillary structures, with scant fibrous stroma and extensive hemorrhagic areas. Immunohistochemistry showed absence of pituitary hormone expression, PIT-1, SF-1, and neuroendocrine markers, a low proliferative index (Ki-67 ~3%), and strong, diffuse TTF-1 positivity, confirming the diagnosis of PPETS.

Conclusion:
PPETS is an exceptionally rare entity characterized by papillary architecture, low mitotic activity, and lack of pituitary hormonal differentiation. Strong TTF-1 expression represents a significant diagnostic pitfall, particularly in the differential diagnosis with pulmonary or thyroid metastases. This case highlights the importance of integrated clinical, radiological, and pathological assessment for accurate diagnosis of TTF-1–positive sellar lesions.

*Unless otherwise noted, all abstracts presented at ENDO must not be released to the press or the public until the date and time of presentation. For oral presentations, the abstracts are embargoed until the session begins. The Endocrine Society reserves the right to lift the embargo on specific abstracts that are selected for promotion prior to or during ENDO.*