Beyond being transcription factors actively involved in the regulation of gene expression, PRs also act via rapid, extra-nuclear, signaling cascades, such as via the phosphatidylinositol 3-kinase (PI3K)/Akt or the c-Src/extracellular signal-regulated kinases 1/2 (ERK1/2) pathways, playing an important role in breast cancer development [18], [19]. The gene discussed is MAPK3; the disease is breast cancer.