MDM2 and cancer: Further confounding the risk association of cancer with SNP309G is the presence of another MDM2 variant, SNP285C, which is found only in Caucasian populations (~12% of all SNP309G alleles) and strongly reduces the binding of Sp1 to the MDM2 promoter, antagonizing the effects of SNP309G (Paulin et al., 2008; Knappskog et al., 2011; Knappskog and Lonning, 2011).