To understand the role of the hPTTG1/CXCR2 axis in breast cancer development, we orthotopically transplanted control MCF-7Mock cells, MCF-7hPTTG1 cells, and CXCR2-depleted MCF-7hPTTG1 cells into the fourth mammary fat pad of severe combined immunodeficiency (SCID) mice and monitored tumor growth weekly (Figure 5C). The gene discussed is CXCR2; the disease is breast cancer.