*Article* **Tumor Growth Progression in Ectopic and Orthotopic Xenografts from Inflammatory Breast Cancer Cell Lines**

**Sara Caceres 1,† , Angela Alonso-Diez 2,† , Belén Crespo <sup>1</sup> , Laura Peña <sup>2</sup> , Maria J. Illera <sup>1</sup> , Gema Silvan <sup>1</sup> , Paloma J. de Andres <sup>2</sup> and Juan C. Illera 1,\***


**Abstract:** Xenografts can grow in immunosuppressed hosts, such as SCID mice, and tumor material can be injected into hosts either ectopically or orthotopically. Choosing the correct model to use is a crucial step in animal research. The aim of this study was to report the differences between ectopic and orthotopic xenografts in tumor progression, metastasis capacity, histological features, and steroid hormone profiles in xenografts from the cIMC (canine inflammatory mammary cancer) cell line IPC-366 and hIBC (human inflammatory breast cancer) cell line SUM149. To achieve this purpose, 40 female mice 6–8 weeks old were inoculated with IPC-366 and SUM149 cells subcutaneously (ectopic models) or into mammary fat pad (orthotopic models). Mice were monitored for tumor progression and appearance of metastases, and generated tumors were analyzed in terms of histological examination and steroid hormone production. The results revealed differences in tumor appearance and percentage of metastasis between ectopic and orthotopic models, which were higher in the ectopic xenografts from both cell lines. However, both models had similar characteristics of tumor progression, histological features, and steroid hormone secretion profiles. We show that the ectopic model can be validated as a good and useful model of tumor development in addition to, not contrary to, the orthotopic model in breast cancer research.

**Keywords:** xenograft; ectopic; orthotopic; hIBC; cIMC
