The following observations emerged: the study findings support the evidence that PTX3 expression is high in breast cancer patients; PTX3 expression is associated with cancer stemness and epithelial-mesenchymal transition in breast cancer; BmK AGAP down-regulate PTX3 expression in breast cancer in a dose-dependent manner in vitro and in vivo and inhibits stemness and epithelial-mesenchymal transition. Here, PTX3 is linked to breast cancer.