Abstract 3699: Tumor budding: A predictor for metastasis in the CAM xenograft model
Authors: Muenzner Julienne K. , Ranjan Raphela A. , Eckstein Markus , Erber Ramona , Kunze Philipp , Geppert Carol I. , Ruebner Matthias , Baeuerle Tobias , Hartmann Arndt , Schneider-Stock Regine 
Published: August 2019

Abstract
Background: Nowadays, breast cancer represents both the most frequently diagnosed type of cancer as well as the leading cause of cancer associated death in women. Clinically, breast cancer tumors can be stratified into four major subgroups based on the expression of estrogen receptors (ER) and progesterone receptors (PR), the proliferation marker Ki67 and the expression/amplification of HER2/neu. Hormone receptor (HR) positive tumors generally have a slightly more favorable prognosis than the other two subgroups and can be treated with agents interfering with hormone signaling. A targeted therapy approach is also applied for HER2/neu amplified tumors by using agents that inhibit HER2/neu. In contrast, patients with triple negative breast cancers (TNBCs), i.e. tumors lacking HR expression as well as HER2/neu amplification, have a fairly poor outcome due to the high aggressiveness of this subgroup, especially if not responding to neoadjuvant therapy.
Methods: In our study, we investigated phenotypical and functional characteristics of the two breast cancer cell lines MCF-7 and MDA-MB-231 that resemble the HR+ and the TNBC subgroup, respectively. In vitro, we were specifically interested in the invasiveness of the cells, thus determining their aggressiveness in a 3D spheroid invasion assay. In addition, we applied the in vivo chorioallantoic membrane (CAM) xenograft assay to histologically analyze the tumor growth patterns and evaluate metastasis formation using a human-specific Alu-PCR method and an in vivo imaging system (IVIS).
Results: As anticipated, the highly aggressive TNBC cell line MDA-MB-231 generated CAM micro-tumors much larger than those derived of the HR+ MCF-7 cell line. Moreover, we were able to verify different characteristic histological features of TNBC and HR+ tumors in the CAM xenograft model. In this regard, the MDA-MB-231 cells showed the distinct growth pattern of a poorly differentiated adenocarcinoma and a highly infiltrative growth into the CAM with strong tumor budding (clusters of ≤5 cells) at the invasive front. The high tumor budding rate could be correlated to an extremely invasive potential of the TNBC cells in vitro as well as to a strong metastasis formation in the in vivo CAM assay.
Conclusion: Our findings suggest that the CAM xenograft assay represents a suitable model to mimic the clinical situation of breast cancer patients. For the first time, we could show that tumor budding is correlated with metastasis formation in this alternative xenograft system.
Citation Format: Julienne K. Muenzner, Raphela A. Ranjan, Markus Eckstein, Ramona Erber, Philipp Kunze, Carol I. Geppert, Matthias Ruebner, Tobias Baeuerle, Arndt Hartmann, Regine Schneider-Stock. Tumor budding: A predictor for metastasis in the CAM xenograft model [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3699.