This compound inhibits breast cancer cell proliferation and mammosphere formation in a dose-dependent manner and reduces the CD44high/CD24low subpopulation and aldehyde dehydrogenase (ALDH)-expressing cell population as well as the expression of the self-renewal-related genes CD44, SOX2, and OCT4.3-O-p-Coumaroyltormentic acid preferentially reduced the protein levels of c-Myc, which is a CSC survival factor, by inducing c-Myc degradation. This evidence concerns the gene SOX2 and breast cancer.