POSTN and osteosarcoma: Analogously, inhibition of periostin gene expression suppresses the proliferation and invasion of U2OS osteosarcoma cells [41] Our immunohistochemical finding of increased expression of periostin at the edge of growing bone tumours is in keeping with a role for periostin in tumour growth and, taken with the results of previous studies, suggests that periostin could represent a potential therapeutic target to control the growth of osteosarcoma and other bone tumours.