The Chorioallantoic Membrane Xenograft Assay as a Reliable Model for Investigating the Biology of Breast Cancer

SIMPLE SUMMARY: The chorioallantoic membrane (CAM) is a highly vascularized membrane found in avian eggs. Tumor cell lines can be grown on the CAM, which allows for the further analyses of the tumor grafts afterwards. We investigated the biological and growth characteristics of two breast cancer cell lines that resemble two biologically different breast cancer subgroups. Known biological features of the more aggressive breast cancer cell line were clearly confirmed in vitro and in the CAM model. Furthermore, the tissue-based pathological variables assessed in the CAM model were similar to those of the mouse xenografts and human patient tumor tissue. We suggest this in vivo model to be a reliable alternative for breast cancer research to reduce murine animal experiments. ABSTRACT: The chorioallantoic membrane (CAM) assay is an alternative in vivo model that allows for minimally invasive research of cancer biology. Using the CAM assay, we investigated phenotypical and functional characteristics (tumor grade, mitosis rate, tumor budding, hormone receptor (HR) and HER2 status, Ki-67 proliferation index) of two breast cancer cell lines, MCF-7 and MDA-MB-231, which resemble the HR+ (luminal) and triple-negative breast cancer (TNBC) subgroups, respectively. Moreover, the CAM results were directly compared with murine MCF-7- and MDA-MB-231-derived xenografts and human patient TNBC tissue. Known phenotypical and biological features of the aggressive triple-negative breast cancer cell line (MDA-MB-231) were confirmed in the CAM assay, and mouse xenografts. Furthermore, the histomorphological and immunohistochemical variables assessed in the CAM model were similar to those in human patient tumor tissue. Given the confirmation of the classical biological and growth properties of breast cancer cell lines in the CAM model, we suggest this in vivo model to be a reliable alternative test system for breast cancer research to reduce murine animal experiments.