SPP1 and neoplasm: Moreover, the observation that OPN protein or gene expression levels are increased in many human tumours, including breast (Tuck et al, 1997; Tuck and Chambers, 2001), lung (Chambers et al, 1996), prostate (Thalmann et al, 1999), colon (Agrawal et al, 2002), ovarian (Kim et al, 2002) and gastric (Ue et al, 1998) cancer, confirmed the hypothesis that it plays an important role in tumorigenesis, tumour progression and metastasis (Oates et al, 1997; Furger et al, 2001).