Abstract A017: Epigenetic Activation of SOX11 is Associated with Recurrence and Progression of DCIS to Invasive Breast Cancer

Abstract Background: Screening mammography has dramatically increased incidental detection of Ductal Carcinoma in situ (DCIS), a non-obligate precursor of breast cancer. Approximately 10-50% of DCIS progress to the invasive disease and the risk of developing recurrence or progression after surgery is still not well defined based on clinical and pathological characteristics. Our study investigated the genetic and epigenetic mechanisms associated with recurrence and progression of DCIS to invasive cancer. Methods: To identify genes associated with recurrence and progression of DCIS to invasive cancer, we performed Nanostring nCounter analysis (MDACC, n = 40) and RNA-sequencing (Sloane study, n = 183) in two independent prospective primary DCIS cohorts. Mammary epithelial-specific Pten knockout mouse model developed in our lab was used to interrogate the genetic pathway deregulated during development of mammary intraepithelial neoplasia to adenocarcinoma. ATAC-seq and ChIP-qPCR were performed to assess chromatin accessibility in the genome and validate binding of histone-modifying enzymes on target promoters. Histopathological analyses were performed to determine DCIS grades, subtypes, and protein expression profiles. Results: RNA expression profiles of normal mammary and primary DCIS tissues (n = 40) identified 10 gene transcripts that were significantly and differentially expressed between normal and high-grade DCIS. Only SOX11 expression was significantly and progressively correlated with KI67 and the DCIS recurrence score as described by Solin (JNCI 2013). Mammary intraepithelial neoplasia in Pten knockout mice and 21T DCIS to IDC progression cell line model also revealed SOX11 upregulation compared to controls. Since PTEN/PI3K/AKT pathway is known to regulate global active histone marks and open accessible chromatin, we investigated the role of AKT on SOX11 expression. Results demonstrated that inhibition of AKT altered enrichment of histone-modifying enzymes KDM5A and EZH2 on the promoter accompanying downregulated SOX11 expression in DCIS cell lines. SOX11 and EZH2 expression profiles revealed significant correlation in DCIS tissue samples. In two independent DCIS cohorts, SOX11 was found significantly upregulated in HER2+ and basal-like DCIS subtypes (P < 0.001). RNA sequencing in 183 longitudinal DCIS cases of the Sloane study (median follow-up of 96 months) revealed significantly shorter recurrence-free survival in SOX11+ than SOX11- patients (P < 0.02 in all subtypes; P = 0.002 in HER2+ subtype). Based on COX proportional hazards model, SOX11 alone was significantly associated with the risk of developing recurrence and invasive breast cancer (HR = 1.7, 95% CI = 1.1 to 2.6; P < 0.02). Conclusions: Epigenetic activation of SOX11 is associated with recurrence and progression of DCIS to invasive breast cancer. SOX11 and its epigenetic regulators can be developed as prognostic markers for DCIS patients with recurrence risk independent of traditional clinical and pathologic characteristics. Citation Format: Warapen Treekitkarnmongkol, Vandna Shah, Kazuharu Kai, Hiroshi Katayama, Justin W. Wong, Farah A Ladha, Brian Menegaz, Sarah E. Pinder, Wei Lu, Fei Yang, Ximing Tang, Savitri Krishnamurthy, Ignacio I. Wistuba, Elinor J. Sawyer, Alastair M. Thompson, Subrata Sen. Epigenetic activation of SOX11 is associated with recurrence and progression of DCIS to invasive breast cancer [abstract]. In: Proceedings of the AACR Special Conference on Rethinking DCIS: An Opportunity for Prevention?; 2022 Sep 8-11; Philadelphia, PA. Philadelphia (PA): AACR; Can Prev Res 2022;15(12 Suppl_1): Abstract nr A017.