CEACAM21 is a cell adhesion molecule belonging to the carcinoembryonic antigen-related cell adhesion molecule family, localized to the external plasma membrane with roles in immune response and T cell activation 1. In cancer biology, CEACAM21 expression is functionally implicated in tumor progression: genetic variants at the 19q13 locus (rs11672691) that increase CEACAM21 transcript levels are associated with aggressive prostate cancer phenotypes through altered HOXA2 transcription factor binding, with CRISPR-validated direct effects on cellular aggressiveness 2. CEACAM21 is significantly overexpressed in immune-active high-grade serous ovarian cancer tissues compared to immune-silent tumors, suggesting a role in tumor immunoediting 3. Beyond oncology, CEACAM21 has been identified as a schizophrenia susceptibility locus (rs4803480) in family-based genome-wide association studies, replicated across Jewish-Israeli and Arab-Israeli populations 4. A long noncoding RNA transcribed from the CEACAM21 locus (lncCEACAM21) shows decreased expression in severe COVID-19 cases and correlates inversely with neutrophil/lymphocyte ratios, suggesting biomarker potential for disease severity stratification 5. Notably, CEACAM21 showed no significant association with type 1 diabetes susceptibility in large consortium studies 6. These findings establish CEACAM21 as a multifaceted immune-related molecule with implications in cancer immunotherapy and infectious disease severity.