Using the Topflash/Fopflash dual-luciferase reporter assay—a specific tool for monitoring Wnt/β-catenin pathway activity—we found that SAMD4B knockdown significantly reduced Topflash reporter activity in both MCF-7 and MDA-MB-231 breast cancer cells, whereas SAMD4B overexpression markedly enhanced Topflash reporter activity. This evidence concerns the gene SAMD4B and breast cancer.