In mesothelioma, positive markers, such as CK5/6, calretinin, WT‐1, HBME‐1, thrombomodulin, mesothelin and D2‐40, are commonly used, and negative markers such as TTF‐1, CEA, MOC31, BG8 and Ber‐EP4 are rarely expressed.4, 5. Here, PTGER4 is linked to mesothelioma.