Taking into account that EP4 antagonists at therapeutic doses are well-tolerated, a phase II trial is currently evaluating the potential of the GW627368X-derived EP4 antagonist AAT007 (also known as RQ-07 or grapiprant, Galliprant®, Figure 3b) with respect to circulating tumor cells and the improvement of outcome in advanced prostate, breast and non-small cell lung cancer alone or in combination with gemcitabine. Here, PTGER4 is linked to neoplasm.