Abstract 5199: Microenvironmental control of breast cancer subtype elicited by paracrine platelet-derived growth factor-CC signaling

Aim: Breast tumors of the basal-like, hormone receptor-negative subtype, remain an unmet clinical challenge, as patients exhibit the highest recurrence rate, the shortest time to recurrence and the worst overall survival rate due to a paucity of therapeutic targets. Also, as tumors develop, the surrounding microenvironment co-evolves into an activated state through continuous paracrine communication, creating a dynamic signaling circuitry that promotes malignant progression. Thus, novel treatment approaches that also include the targeting of stromal components are urgently required. Methods: We used experimental mouse models of cancer (transgenic, syngeneic, human cell lines and patient-derived xenografts) for knockout studies and preclinical trials, immunostaining, in vitro assays, western-blot, gene expression analysis and RNA-sequencing, patient cohorts, data mining and bioinformatics analysis. Results and discussion: We identified a paracrine crosstalk between cancer cells expressing platelet-derived growth factor (PDGF)-CC and cancer-associated fibroblasts (CAFs) expressing the cognate receptors in human basal-like mammary carcinomas. In translational efforts, we found that PDGF-CC expression in the malignant epithelium of breast cancer was associated with a hormone receptor-negative state. We then generated a mouse model to characterise the functional role of PDGF-CC in tumorigenesis. Moreover, we identified and validated factors secreted by CAFs to maintain a basal-like phenotype, e.g. Stanniocalcin (STC)-1, Hepatocyte Growth Factor (HGF) and Insulin Growth Factor Binding Protein (IGFBP)-3. Genetic or pharmacological targeting of PDGF-CC in experimental mouse models resulted in the transcriptional reprogramming and conversion of basal-like breast tumors into a luminal-like state characterised by Estrogen Receptor (ER)-α positivity, that conferred sensitivity to endocrine therapy in previously intrinsically unresponsive tumors. Conclusions: Specification of the basal-like subtype of breast cancer is under microenvironmental control and therapeutically actionable in order to achieve sensitivity to endocrine therapy. Our work sheds light on previously unknown mechanisms that define breast cancer subtype and has significant therapeutic implications for patients with basal-like breast tumors. Citation Format: Matteo Bocci, Michael Bartoschek, Pernilla Roswall, Kristian Pietras. Microenvironmental control of breast cancer subtype elicited by paracrine platelet-derived growth factor-CC signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5199.