Abstract 4092: Tumor cell JAG1 promotes lymph node metastasis and predicts recurrence in lymph node positive breast cancer patients

Abstract Lymph node metastasis is a “canary in the coal mine” in breast cancer, acting as a distinct prognostic indicator of aggressive disease. In preclinical models, invasion of tumor cells into lymphatics and lymph nodes is promoted by LECs that are active participants in the promotion of tumor cell invasion. It remains unclear how breast tumors interact with LEC cell signaling pathways to transverse lymphatic endothelium. Better understanding of specific and clinically actionable mechanisms that tumor cells use to promote lymphogenous metastasis are needed to reduce disease progression to distant organs. Expression of the Notch ligand JAG1 has long been associated with poor prognosis in patients, and JAG1 has been established to have critical roles in lymphatic specification and development. Using mouse models, we report that JAG1 expression in tumor cells actively promotes lymph node metastasis. JAG1 expression in tumor cells promotes progression through multiple stages of the lymphogenous metastatic cascade, including lymphovascular invasion into peritumoral lymphatic vessels, entry to mammary lymphatic collecting ducts, invasion into the subcapsular sinus of the lymph node, and overt nodal metastasis. To understand the underlying mechanisms of JAG1-driven metastasis, we determined that exposure of LECs to JAG1, either by JAG1-expressing tumor cells or tethered exogenous ligand, disrupted lymphatic barrier integrity and increased tumor cell migration across LEC monolayers in vitro. JAG1-stimulated transendothelial tumor migration could be suppressed with a Notch4-inhibiting antibody, but was not affected by treatment with a canonical Notch inhibitor. We demonstrated that JAG1 expression in tumor cells promotes VEGFR3 activity in LECs. JAG1-dependent lymph node metastasis can be suppressed with two distinct soluble VEGFR3 antagonists in vivo. In human synchronous breast and lymph node samples from node positive patients, we demonstrate that tumor cells in the lymph node are enriched in JAG1 compared to the primary tumor. Enrichment of JAG1 in lymph nodes was clinically meaningful, as JAG1 levels in the node, but not the primary tumor, predicted disease recurrence post-lumpectomy, which suggests that molecular workup of sentinel lymph nodes may be informative in lymph node positive patients. These data provide a novel mechanism by which tumor cells regulate cell behaviors in nearby lymphatic endothelium to promote invasion and lymphogenous metastasis. Citation Format: Benjamin Gordon, Seock Won Youn, Bhairavi Swaminathan, Natalia Obacz, Rahul Vadakath, Pamela Teneqexhi, Isabel Alvarez-Lopez, Marta Rezola, Sara Manzano, Zuhara Telletxea, Ziqiao Xu, Zhengjia Chen, Ekrem Emrah Er, L. A. Naiche, María Muñoz Caffarel, Jan Kitajewski. Tumor cell JAG1 promotes lymph node metastasis and predicts recurrence in lymph node positive breast cancer patients [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 4092.