Bautista et al (1996) developed the first ELISA able to quantify OPN levels in blood plasma and using this assay they measured baseline levels in a series of normal women. Singhal et al (1997) then used this ELISA to quantify OPN plasma levels in 70 women with metastatic breast cancer compared to healthy women and women on well follow-up for cancer. Osteopontin plasma levels were significantly elevated in women with metastatic breast cancer, relative to either control group (P<0.001). This evidence concerns the gene SPP1 and cancer.