SPP1 and neoplasm: When tumor tissue OPN positivity was defined and assessed as the percentage of cells staining by IHC as a continuous variable (regardless of intensity), of the 462 primary tumors assayed, the mean percentage of OPN tumor cell positivity was 33.9 (95% CI: 30.2 to 37.9), and was not significantly different for 105 patients who subsequently developed recurrence (32.4 (95% CI: 24.6 to 41.2)) and the 357 who did not (34.4 (95% CI: 30.2 to 38.8)).