It has been discovered that cigarette smoke extract exposure induces morphological changes of human BC T24 cells, with enhanced cell migration and invasion, reduced epithelial marker expression and increased mesenchymal marker expression, resulting in the activation of the ERK1/2 (Extracellular Signal-regulated Kinase 1 and 2) pathway as well as of the activator protein 1 (AP-1) [20]. This evidence concerns the gene MAPK3 and breast cancer.