SAT-165 Sterol O-Acyl Transferase 1 as a Prognostic Marker of Adrenocortical Carcinoma

Background: Adrenocortical carcinoma (ACC) is a rare endocrine malignancy with an unfavorable prognosis. Despite the poor prognosis in the majority of patients, no improvements in treatment strategies have been achieved, largely due to the rarity of these tumors. Therefore, the discovery of new prognostic biomarkers that could guide and improve the management of patients with ACC is of enormous interest. Sterol-O-Acyl Transferase 1 (SOAT1) is involved in cholesterol esterification in adrenocortical cells. Recently, it was demonstrated that SOAT1 inhibition leads to impaired steroidogenesis and cell viability in ACC [1]. There are no studies so far addressing the impact of SOAT1 protein expression in ACC prognosis and clinical outcomes. Methods: We evaluated SOAT1 protein expression by immunohistochemistry (ab39327; 1:4000; Abcam, EUA) in a tissue microarray of 107 adrenocortical carcinomas (Weiss score ≥ 3) from adult patients treated in a single tertiary center in Brazil. Immunohistochemistry results were evaluated through a semiquantitative approach by two independent pathologists. We aimed to evaluate the correlation of SOAT1 protein expression with clinical and biochemical parameters, surgical specimen histological characteristics, recurrence free-survival, progression free-survival and overall survival. Results: SOAT1 protein expression was heterogenous in this cohort; 38% of ACCs demonstrated strong SOAT1 protein expression while 62% demonstrated weak or absent SOAT1 protein expression. Strong SOAT1 protein expression correlates with known features of high aggressiveness in ACC, such as excessive tumor cortisol secretion (p= 0.007), advanced disease stage [ENSAT 3 and ENSAT 4 (p= 0.009)] and high Ki67 index (0.008). On multivariate analysis, strong SOAT1 protein expression was an independent predictor of lower overall survival (HR 1.71, CI 95% 1.05-2.92; p= 0.04) when considering all cases (n= 107) and of lower progression free survival (HR 3.05, CI 95% 1.05-8.85; p= 0.04) in patients with metastatic disease at diagnosis (n= 22). Conclusions: Our findings demonstrated that SOAT1 protein expression has prognostic value in ACC and reinforce the importance of investigating SOAT1 as a possible therapeutic target for patients with ACC. Multicentric prospective studies including a larger number of patients are needed in order to validate and consolidate the results found in this cohort. References: 1. Sbiera S, Leich E et al. Mitotane inhibits Sterol-O-Acyl Transferase 1 Triggering Lipid-Mediated Endoplasmic Reticulum Stress and Apoptosis in Adrenocortical Carcinoma Cells. Endocrinology. 2015; 156 (11):3895-908.