In MMTV-PyMT carcinoma-derived pB1.3G cells and MDA-MB-231 (M.D. Anderson Metastatic Breast cancer cell line established from a pleural effusion of a 51-year-old female with highly aggressive and poorly differentiated triple-negative ductal cancer) human breast cancer cells, the knockdown of Snail1 attenuates primary tumor growth, strongly suppresses its metastatic spreading, and induces the acquisition of epithelial traits in a reverse epithelial-mesenchymal transition process [24]. The gene discussed is SNAI1; the disease is Pleural effusion.