Endocrine Abstracts

JOINT3711

Introduction: Folliculo-stellate cells (FSCs) are nonsecretory cells located in the anterior pituitary gland, having a star-like appearance and the ability to form follicles. They represent a heterogeneous population in terms of both phenotype and function. FSCs form a support network and regulate endocrine cells activity by producing numerous paracrine factors. Furthermore, they might be involved in the pathogenesis of pituitary neuroendocrine tumors (PitNETs).

Materials and Methods: Eight patients with Cushing’s disease were included in the study. The tumor specimens were obtained after transsphenoidal surgery. The preoperative diagnosis was supported by clinical features, hormonal assessment, and radiological evaluation (contrast-enhanced pituitary magnetic resonance imaging, MRI). The histopathological diagnosis was performed using hematoxylin eosin morphological staining. Reticulin staining was applied for reticulin fibers evaluation. Immunohistochemical (IHC) evaluation for anterior pituitary hormones (GH, PRL, ACTH, TSH, FSH, LH) and transcription factors (PIT1, TPIT, SF-1) were assessed to perform an adequate classification of the tumors. FSCs were analyzed using glial fibrillary acidic protein (GFAP).

Results: Histopathological evaluation revealed acidophilic tumor cells with a diffuse growth pattern. All cases had IHC positive reaction for ACTH and TPIT. In addition, three cases showed positive IHC expression for GH and PIT1. According to current WHO classification, these were considered PitNETs with unusual IHC combination (TPIT/PIT1 positive). Morphologically FSCs were star shaped, with long cytoplasmic prolongations among the tumoral cells. GFAP positive cells were identified in all PitNETs, with high heterogeneity regarding the distribution pattern and intensity of the reaction. Two of the corticotropinomas presented only a few isolated positive FCSs with a low intensity of the IHC expression. Five of the cases showed GFAP positive cells distributed in small groups/nests among tumoral cells. In only one of the tumors, FSCs were organized in a wide and dense network. Moreover, the tumors classified as PitNETs with unusual IHC combination (TPIT/PIT1 lineage) presented GFAP positive cells located in the vicinity of blood vessels, having close contact with the endothelial cells.

Conclusion: FSCs represent non-secretory cells occupying approximately 5-10% of the anterior pituitary lobe. In our cases, they showed a wide variability regarding the distribution pattern and intensity of reaction. TPIT/PIT1 positive tumors presented a high density of FSCs. The strong connection between FSCs and blood vessels in TPIT/PIT1 positive PitNETs may contribute to the selection of two different cell lineages. Further studies are needed to establish the connection between these cells and PitNETs.