WFDC1 (WAP four-disulfide core domain 1) encodes ps20, a secreted protein that functions as a growth inhibitor and modulator of inflammatory responses. The protein contains four disulfide bonds formed by eight cysteine residues and exhibits characteristics of serine protease inhibitors 1. WFDC1 has growth inhibitory activity and was first characterized as a secreted growth inhibitor from fetal urogenital sinus mesenchymal cells 2. The protein regulates cell adhesion, migration, and proliferation, and can stimulate angiogenesis through effects on endothelial cell migration and pericyte stabilization 1. Mechanistically, WFDC1 functions as a matricellular protein that modulates inflammatory and wound repair responses by regulating osteopontin and matrix metallopeptidase-9 (MMP-9) activity 3. WFDC1-null mice show enhanced wound healing rates and altered immune responses, including reduced viral titers in influenza infection 3. The gene maps to chromosome 16, a region of frequent loss of heterozygosity in multiple cancers 4. WFDC1 expression is downregulated in various cancers including prostate cancer and melanoma, where it appears to function as a tumor suppressor 56. Clinical significance includes potential roles as therapeutic targets and biomarkers for cancer diagnosis and treatment 1.