Abstract A007: Single nuclei analysis of uterine serous carcinoma reveals racial differences in immune signaling

Abstract Endometrial cancer (EC) is a growing public health concern, as incidence rates continue to rise every year. Even more troubling is the unequal survival rates between racial groups with EC, as Black EC patients are dying at twice the rate of white EC patients. Uterine serous carcinoma (USC) is an aggressive subtype of EC that affects Black patients more frequently than white patients. While USC accounts for only 10-15% of all reported EC cases, it has a disease specific mortality rate of over 40%. It is currently unclear what is causing the racial differences in subtype frequency and survival rate of USC. To gain insight on the transcriptomic differences of tumor cells and cells within the tumor microenvironment (TME), we performed single-nuclei RNA sequencing of 13 USC tumors, with 9 tumors from Black patients and 4 from white patients. We found significant gene expression differences, including the upregulation of PAX8 in tumors of Black patients. PAX8 is a lineage factor important in Mullerian duct tissues and is frequently upregulated in EC. In PAX8 high tumor cells, signaling pathways such as TGBF, JAK- STAT, and NFKB activity was enriched, while PAX8 low cells were enriched for p53, WNT, and estrogen signaling. To understand if PAX8 directly affects epithelial immune signaling, we performed RNA-seq on PAX8 knock down (KD) ARK2 cells. Analysis of DEGs showed that PAX8 KD cells express high IL-1A and IL-1B, while chemokines such as CXCL1 and Midkine were downregulated. When conditioned media (CM) from PAX8 KD cells were added to THP-1 macrophages, decreased levels of anti-inflammatory markers such as ARG1 and TGFB1 were observed, compared to PAX8 expressing cells. Additionally, pro-inflammatory molecules such as TNFa and IL-6 were expressed at higher levels. These observations were validated by a cytokine antibody array; macrophages treated with PAX8 KD CM secreted higher levels of pro- inflammatory cytokines such as IL-1A, IL-1B, IL-6, and CXCL5. Anti-inflammatory molecules such as TGFB1 and TGFB2, and growth factors such as FGF6 and FGF7, were secreted at lower levels than control. These studies indicate that PAX8 is a novel regulator of the epithelial- immune axis, which is upregulated in USC compared to normal tissue and modulates the TME in favor of immune suppression and tumor growth. Because PAX8 expression is higher in tumors of Black patients compared to white, this may indicate that Black patients have a higher degree of immunosuppression. Our studies are the first to report tumor differences between Black and white USC patients at the single nuclei level. Additionally, we report findings from the first study to use single nuclei sequencing to study a tumor from Black USC patients. Our results indicate that taking race into account when determining treatment for USC may improve outcomes for Black patients. Citation Format: Grace Foley, J. Julie Kim. Single nuclei analysis of uterine serous carcinoma reveals racial differences in immune signaling abstract. In: Proceedings of the AACR Special Conference on Endometrial Cancer: Transforming Care through Science; 2023 Nov 16-18; Boston, Massachusetts. Philadelphia (PA): AACR; Clin Cancer Res 2024;30 (5Suppl): Abstract nr A007.