SPP1 and neoplasm: Other properties that can be affected by an increase in osteopontin expression include an increase in matrix metalloproteinase expression (Teti et al, 1998), an increase in cellular migration (Liaw et al, 1994; Tuck et al, 2000) and a protective capacity of tumour cells from macrophage-mediated nitric oxide attack (Denhardt and Chambers, 1994; Feng et al, 1995).