Fourth, increased biliary expression of caspases 1 and 4 and of IFN-γ–related and tumor necrosis factor-alpha (TNF-α)–related genes in neonatal mice with experimental BA on the one hand, and parallel studies in the liver from affected children showing increased expression of pro-apoptosis molecules on the other hand, underscore apoptosis as a significant mechanism of injury to duct epithelium in BA. The gene discussed is TNF; the disease is breast angiosarcoma.