Moreover, we observed a marginal decrease in the proliferation of non-TNBC cell lines upon the downregulation of TBC1D9. However, an increase in migratory and tumorigenic potential was observed upon knockdown (KD) of TBC1D9 in both non-TNBC and TNBC cell lines by regulating the expression of ARL8A, PLK1, HIF1α, STAT3, and SPP1. The present study sheds light on the role of TBC1D9 as a modulator of BC aggressiveness and underlines the fact that the aggressiveness of TNBC could be due to the lack of expression of TBC1D9. This evidence concerns the gene SPP1 and breast cancer.