Abstract 4861: Triple-negative breast cancers establish a systemic environment that drives malignant progression of otherwise indolent disseminated tumors via EGF and IGF

Breast cancer recurrence rates are variable, suggesting that tumor cells disseminate from primary sites at an early stage but remain indolent for extended periods of time before progressing to symptomatic disease. Little is known about mechanisms that cause otherwise dormant tumors to become overt cancers, making it difficult to predict which breast cancer patients are likely to relapse and therefore likely to benefit from preemptive therapy. To address these challenges, we use a human breast tumor xenograft model in which aggressively growing breast cancers (“instigators”) promote the growth of otherwise indolent breast cancers (“responders”) that have disseminated to distant sites. These pro-tumorigenic systemic effects are established by instigating tumors, in large part, through their mobilization of bone marrow cells (BMCs) that are subsequently recruited to the responding breast tumors, where they create a tumor-supportive microenvironment. We report here that the mechanisms of establishing tumor-supportive systemic environments depend upon the molecular-histopathological subtype of the instigating breast cancer. Instigating cell lines and primary tumor surgical specimens, derived from patients with either triple-negative breast cancer (TNBC) or luminal breast cancer (LBC), established different subtype-specific systemic environments that impinged in different ways upon the malignant features of responding tumor cells and their microenvironment. In particular, the TNBC-induced responding tumor microenvironment was characterized by elevated levels of epidermal growth factor (EGF) and insulin-like growth factor 1 (IGF1). EGF and IGF acted on responding tumor cells in a paracrine manner to induce expression of factors that play a role in tumor-initiation, embryonic stem cell maintenance, and epithelial-mesenchymal transition. Pharmacological administration of EGFR and IGF1R inhibitors prevented responding tumors from acquiring the TNBC-induced malignant features, thus maintaining them in an indolent state. Our results demonstrate that microenvironmental composition, as well as tumor cell phenotypic plasticity and molecular properties, are strongly influenced by the host systemic macroenvironment. Our work suggests that the crosstalk between disseminated tumor cells and their microenvironment can be exploited therapeutically to improve outcomes for patients with TNBC. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd A