Purpose: Histological studies have shown that the two sialoproteins, bone sialoprotein (BSP) and osteopontin (OPN), are induced in multiple types of cancer. We have recently found that these proteins are bound in serum to complement factor H and that the complex must be disrupted to generate free protein to measure their total levels. We hypothesized that measuring total BSP and OPN levels would provide informative markers for the detection of cancer.
Experimental design: As a proof of concept study, serum from patients with diagnosed breast, colon, lung, or prostate cancer (n = 20 for each type) as well as normal serum (n = 77) were analyzed using competitive ELISAs developed for BSP and OPN. Sensitivity, specificity, as well as positive and negative predictive values were determined for each sialoprotein and cancer type. The relationship between sensitivity and specificity was profiled by receiver operating characteristic curves.
Results and conclusions: Determined values for serum BSP in ng/ml were 285 +/- 19 for prostate, 373 +/- 19 for colon, 318 +/- 18 for breast, 155 +/- 11 for lung cancer sera, and 154 +/- 13 for normal sera. Values of OPN in ng/ml were 653 +/- 39 for prostate, 449 +/- 22 for colon, 814 +/- 53 for breast, 724 +/- 33 for lung, and 439 +/- 30 for normal sera. The assays provide a high degree of sensitivity and specificity that enables the detection of colon, breast, prostate, and lung cancer.