PLAC1 (placenta-enriched 1) is an X-linked, cancer-testis-placenta (CTP) antigen with dual roles in placental development and cancer progression. During normal pregnancy, PLAC1 is exclusively expressed by trophoblast cells throughout gestation and localizes to the syncytiotrophoblast microvillous membrane 1. Its expression is stimulated by keratinocyte growth factor, suggesting involvement in placental growth and differentiation 1. However, PLAC1 is aberrantly expressed in diverse human cancers including head and neck squamous cell carcinoma (HNSCC), breast, prostate, and colorectal cancer 23. In HNSCC, PLAC1 promotes tumor progression by inducing epidermal growth factor receptor endocytosis and recycling to enhance PI3K/AKT signaling 4. SP1 transcription factor regulates PLAC1 expression in cancer cells 4. PLAC1+ tumor cells establish a reciprocal protumor loop by recruiting CD4+ T cells via CXCL11/CXCR3 and inducing Treg differentiation via PVR/TIGIT 4. Elevated PLAC1 expression in colorectal cancer liver metastases correlates with poor prognosis and metastatic potential 5. Given its restricted normal expression and cancer association, PLAC1 represents a promising immunotherapeutic target for personalized cancer treatment 36.