We evidenced the existence of a CD1/Cdk4/Pxn axis that is the specific target of a ligand-activated PR-B signal, inhibiting Rac activity, thus we elucidated a novel mechanism regulating the mesenchymal-epithelial transition in breast cancer cells, further confirming the OHPg/PR-B protective effects in breast cancer. The gene discussed is PXN; the disease is breast carcinoma.