SPP1 and breast carcinoma: Our results indicated that TCF4 shRNA-1105 could downregulate the expression of OPN, consistent with other studies reporting that TCF 4 can regulate OPN expression in a Wnt-dependent manner to act as a repressor or activator in breast cancer progression [25] and that the β-catenin/TCF4 transcriptional complex regulates OPN expression [23].