Furthermore, treatment of Ha-ras-transformed metastatic human keratinocytes, RT3 cells, cocultured in spheroids with human skin fibroblasts with the C5aR1 ligand rhC5a significantly enhanced the invasion of RT3, UT-SCC-115, and UT-SCC-7 cells through collagen I. These results suggest that the interaction between fibroblasts and cancer cells is necessary to induce the expression of C5aR1 by cSCC cells and that C5aR1 promotes the invasion of cSCC cells. The gene discussed is C5AR1; the disease is cancer.