SPP1 and neoplasm: In experiments examining parallel ras-transformed 3T3 cell lines from wild-type (WT) and OPN-deficient mice, the transformed properties of the OPN-deficient cells were uniformly attenuated as compared to WT (Wu et al, 2000): both growth of primary tumours arising from cells injected subcutaneously as well as experimental metastasis were reduced in OPN-deficient cells.