PLAC9 (placenta associated 9) is a putative secretory protein initially identified as placenta-enriched 1, localized to the cytoplasm with classical endoplasmic reticulum-Golgi secretory pathway characteristics 2. The protein contains a signal peptide and coiled-coil segment 1, and functions through protein binding interactions [GO annotation]. PLAC9 exhibits dual regulatory roles in cell biology: it inhibits cell proliferation through S-phase and G2/M arrest via altered cyclin/CDK expression 32, while simultaneously promoting cell motility and migration through coordinated actions involving E-cadherin and vimentin 3. In prostate cancer, PLAC9 is identified as a tumor endothelial cell marker associated with the tumor microenvironment 4. PLAC9 shows reduced expression in lung adenocarcinomas compared to normal tissue, suggesting tumor suppressor properties 3. Clinically, PLAC9 is part of a 7-gene prognostic signature for bladder cancer prognosis 5. Additionally, PLAC9 has been identified as a potential transformation marker associated with spontaneous malignant transformation of mesenchymal stromal cells 6. These findings suggest PLAC9 may have therapeutic relevance in multiple cancer contexts through modulation of proliferation and motility pathways.