Moreover, TrkB-induced AKT activation and cyclin D1 expression were significantly reduced in c-Src-shRNA cells (Figure 1I), indicating that TrkB might be involved in tumorigenicity and metastasis of breast cancer through TrkB-mediated activation of PI3K/AKT and Ras-MAPK pathways or upregulation of cyclin D1 expression. This evidence concerns the gene CCND1 and breast cancer.