COMT and breast cancer: However, neither the case–control study nor the meta-analysis showed any statistically significant association between BC risk and the COMT Val158Met (i.e., a non-synonymous G→A SNP (rs4680, NC_000022.11:19963747:G:A) in exon four leads to a valine (Val) to methionine (Met) peptide change in the mature protein) [60].