As for vascular growth, which is highly correlated with tumor development, bilirubin inhibits ERK activity in damaged blood vessels, and because ERK activation is associated with the mitogenic stimulation-induced cyclin D1 expression (102, 103), the reduction of ERK activity caused by bilirubin may be responsible for the down-regulation of cyclinD1 by bilirubin after arterial injury. The gene discussed is CCND1; the disease is neoplasm.