SPP1 and cancer: In the comparison of low versus intermediate versus high grades, for all cancers combined, the Cochran-Mantel–Haenszel test had for OPN-a M2 = 1.0457, df (degrees of freedom) = 2, p = 0.5928, for OPN-b M2 = 3.2225, df = 2, p = 0.1996 and for OPN-c M2 = 9.7358, df = 2, p = 0.00769.