SPP1 and neoplasm: Mice with debris-stimulated tumors exhibited drastically higher host (murine) OPN levels compared with mice that were injected with either RKO debris alone or the subthreshold inoculum of living RKO cells alone, both of which expressed OPN levels that were comparable to non–tumor-bearing control mice (Fig. 2F, left); however, because RKO does not express OPN (Supplemental Fig. 2C), human OPN was barely detected in the plasma of any of the samples (Fig. 2F, right).