PTGER4 and breast cancer: ,31 EP4, in particular, can activate various intracellular signaling pathways, such as the protein kinase A pathway, adenylate cyclase stimulation, and the cAMP/PKA signaling pathway, thereby promoting the invasive behavior of cancer cells.32, 33, 34 EP4 also plays a significant role in immunosuppression, inhibiting natural killer cell functions in breast cancer,35 recruiting regulatory T cells, and suppressing T cell activation.36