It is mainly secreted by macrophages and can induce cell death of certain tumour cell lines: STEAP, endosomal ferrireductase, functions in erythroid iron homeostasis required for efficient transferrin-dependent iron uptake in erythroid cells; BCL2 (apoptosis regulator), represses apoptosis in various cell systems; inhibits caspase activity; binds to APAF-1. The gene discussed is STEAP1; the disease is neoplasm.