With respect to PC bone metastasis, tumour cells generate several growth factors, such as endothelin 1 (ET-1) and bone morphogenetic proteins (BMPs), that stimulate osteoblastic progenitor cell recruitment and maturation to produce new pathological bone,22 namely, immature mineralised bone (osteoid) around metastasis sites. Here, EDN1 is linked to pachyonychia congenita.