Abstract 1499: Senescent stromal cells drive lung metastases of breast cancer

Abstract In 2022 in the United States, there were nearly 300,000 women diagnosed with breast cancer (BC) with the risk increasing significantly after age 50. The overall 5-year survival rate dramatically decreases, from 99% for patients with stage I, to a devastating 25% for those with stage IV (metastatic) BC, making distal metastasis the leading cause of BC mortality. This mortality rate has not changed in decades with lungs being one of the most common sites for distal metastasis of BC. The BC microenvironment is a complex mix, consisting of tumor cells and numerous nontumor cells including distinct subpopulations of cancer-associated fibroblasts (CAFs): vascular (vCAFs), inflammatory (iCAFs), and myofibroblastic CAFs (myCAFs), which can play pro- or anti-tumor roles. Senescent fibroblasts, which accumulate with age typically express p16INK4A and can modulate the cells around them via the secretion of a cadre of pro-tumorigenic factors including cytokines, chemokines, and extracellular matrix (ECM) modulating enzymes, collectively called the senescence-associated secretory phenotype (SASP). To investigate how p16+ senescent cells impact tumorigenesis, we mated the well-characterized MMTV-PyMT mouse, to the INK-ATTAC (INK) mouse, wherein treatment with AP20187 (AP) selectively eliminates p16+ senescent cells. Preliminary data showed that elimination of p16+ aSMA+ senescent fibroblasts (senCAF) resulted in a significant decrease in primary tumors, lung tumor foci and lung metastatic burden. Further, we found that senescent CAFs (senCAFs) were the only stromal cells eliminated in the PyMT-INK mouse treated with AP, suggesting that this CAF subtype is a key contributor to tumor progression. To determine if senCAFs directly impacted lung metastasis, EO771-LG Luc mammary tumor cells were injected in the tail vein of INKATTAC mice that were treated with AP to eliminate p16+ senCAFs. We found that metastatic tumor burdens were significantly reduced in INK+ versus control mice and immunohistochemical analysis revealed that tumor burden and foci was significantly reduced, suggesting that senCAFs in the lung promoted tumor cell seeding and outgrowth. Citation Format: Anupama Melam, Jiayu Ye, Sheila A. Stewart. Senescent stromal cells drive lung metastases of breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1499.