HTRA3 is one of the four members of the HtrA family proteins, with a secreted multidomain and serine protease activity, which plays an important role in cellular stress response, protein homeostasis, and apoptosis. HTRA3 is highly expressed in the decidual cells in the late secretory phase of the menstrual cycle and throughout pregnancy, and in most trophoblast cell types, apart from the invading interstitial trophoblast during the first trimester. HTRA3 and its family members are down-regulated in several cancers and are proposed as tumor suppressors (PMID: 21321049, 22229724).