Steiner, M.

e17038 Background: Carcinosarcomas (CS) are aggressive gynecologic malignancies defined by a biphasic tumor histology of carcinomatous and sarcomatous components. High expression of glucocorticoid receptor (GR) is associated with aggressive tumor biology in triple-negative breast, ovarian, and endometrial cancers. GR activation results in transcriptional regulation of epithelial-mesenchymal transition (EMT) genes. Therefore, we hypothesized that the sarcomatous component of Müllerian CS may be associated with relatively higher GR expression compared to the carcinomatous portion. Methods: Müllerian CSs from the University of Chicago tissue bank diagnosed from 5/19/2009 – 8/25/2014 were identified and pathology confirmed (RL). In addition, we evaluated GR expression in a mouse PDX CS model. Immunohistochemical expression of nuclear estrogen (ER), progesterone (PR), androgen (AR), and GR was quantified using the H-score. Scores between the sarcomatous and carcinomatous components were compared using a paired t-test. Results: Mean GR H-score was relatively higher in the sarcomatous vs carcinomatous component, overall (144.44 vs 38.89, P = 0.0014). Mean H-score also differed between sarcomatous and carcinomatous components for ER (3.06 vs 63.06, P = 0.016), PR (1.67 vs 47.22, P = 0.004), and AR (0 vs 2.78, P = 0.056). The significantly higher sarcomatous GR expression was replicated in IHC evaluation of the mouse PDX model. Conclusions: GR expression is significantly higher in the sarcomatous than the carcinomatous component of Müllerian CS, while ER, PR, and AR expression is significantly lower. Recent data suggest that an EMT gene signature is more prominently expressed in the sarcomatous versus carcinomatous component. We hypothesize that GR expression and activity may mediate EMT gene expression and represent a therapeutic target for CS. [Table: see text]