There are currently five genes in the REG family found in humans (REG Iα, REG Iβ, REG III, HIP/PAP and REG IV) (9), encoding a growth factor family of proteins involved not only in regeneration of damaged tissues but also in the growth of various types of cancers, including gastrointestinal cancer, cholangiocarcinoma, pancreatic cancer, breast cancer and prostate cancer (10–27). The gene discussed is REG4; the disease is prostate cancer.