Abstract B25: Hormone receptor expression and response in ovarian tumors of low malignant potential

Objective: Primary treatment for ovarian low malignant potential (LMP) tumors is surgical resection with little proven effect of cytotoxic chemotherapy. New therapeutic strategies are needed to prevent and treat recurrence. The objective of this study is to investigate the role of hormone receptors in ovarian low malignant potential tumors. Methods: We obtained formalin-fixed, paraffin embedded (FFPE) tissue samples from patients with ovarian LMP tumors. Clinicopathologic data were collected for all available specimens. Immunohistochemistry (IHC) was performed to determine protein expression. Gene expression was measured using the NanoString nCounter platform. Differences in expression between histologic subtypes were by t-test, followed by a Bonferroni adjustment for multiple comparisons (p Results: Thirty-eight patients were included in this study. The histologic subtypes were divided between 20 serous and 18 mucinous tumors. All serous tumors were ERα and PR positive by IHC and 6 of 20 (30%) were ERβ positive. Only one of the 18 mucinous tumors (5.6%) was positive for both ERα and PR, and all the samples were negative for ERβ. ERβ mRNA levels were elevated in the mucinous LMP tumors and ERα mRNA was higher in the serous samples. ERα and PR protein expression correlated with mRNA expression of ESR1 (r2=0.5606) and PR (r2=0.42), respectively. ERβ expression did not correlate with mRNA expression of ESR2 (r2=0.038). Measurement of estrogen-regulated genes and genes involved in ER signaling (n=236) revealed a clear separation of serous from mucinous subtypes, with 44 genes showing a statistically significant difference (p Conclusion: High levels of ERα, PR, and downstream ERα targets in serous LMP tumors suggest hormone responsiveness and that these tumors are potentially treatable with endocrine therapy. Mucinous tumors largely did not express hormone receptors. In light of this, differences in gene expression observed are more likely attributable to underlying lineage differences than differences in estrogen signaling. Additional large-scale analyses are warranted to better understand the differences between subtypes and to identify avenues for targeted therapy in mucinous LMPs. Citation Format: Sarah E. Taylor, Courtney L. Andersen, Rohit Bhargava, George Tseng, Steffi Oesterreich, Robert P. Edwards, Adrian V. Lee. Hormone receptor expression and response in ovarian tumors of low malignant potential. [abstract]. In: Proceedings of the AACR Conference: Addressing Critical Questions in Ovarian Cancer Research and Treatment; Oct 1-4, 2017; Pittsburgh, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(15_Suppl):Abstract nr B25.