CA7 (carbonic anhydrase 7) is a cytosolic enzyme that catalyzes the reversible hydration of carbon dioxide 1. Located on chromosome 16-23, CA7 is a 263-amino acid protein sharing 50-56% sequence identity with other carbonic anhydrase isozymes 1. CA7 functions within specialized intestinal epithelial cells. BEST4/CA7+ cells represent a novel intestinal cell lineage characterized by CA7 co-expression with BEST4 and other markers 2. These cells play critical roles in fluid homeostasis and immune defense, with CA7 hypothesized to contribute to luminal pH sensing and mucus hydration 2. Upon bacterial infection, CA7-expressing cells generate CFTR-mediated fluid secretion in response to diarrhea-causing toxins, and their expansion is regulated by interferon-γ signaling 3. Clinically, CA7 expression has prognostic significance in colorectal cancer (CRC). Downregulation of CA7 correlates with poor tumor differentiation, lymph node metastasis, advanced TNM stage, and reduced disease-specific survival, particularly in early-stage patients 4. CA7 serves as part of a three-gene signature (CA7, CA2, ITM2C) achieving 100% accuracy for CRC early detection in external validation cohorts 5. These findings suggest CA7 functions as a tumor suppressor in CRC development.