SPP1 and cancer: In the comparison of low versus intermediate versus high stage, for all cancers combined, the Cochran-Mantel–Haenszel test had for OPN-a M2 = 9.57, df = 2, p = 0.008354 (stage M selectively M2 = 7.7651, df = 2, p = 0.0206), for OPN-b M2 = 23.41, df = 2, p = 8.252 × 10–06 and for OPN-c M2 = 19.542, df = 2, p = 5.707 × 10–05 (for OPN-c, stage M selectively M2 = 18.388, df = 2, p = 1.016 × 10–04).