PTGER4 and cancer: Other unresolved mechanisms include: (i) the effects of EP2/EP4 signaling on HB-EGF-mediated cellular signaling; (ii) the involvement of other phospho-proteins identified in our phospho-antibody arrays; (iii) the relationships between EP2/EP4 antagonism and MAP4K3 activation; and (iv) the presence of these molecules in other types of cancer.