Another interesting example for the application of a protein adduct as a biomarker for the internal exposure to an endogenous carcinogen is the quantification of Cys adducts of 17β-estradiol-2,3-quinone and 17β-estradiol-3,4-quinone in Hb of blood samples from breast cancer patients in Taiwan. This evidence concerns the gene GSTM1 and breast carcinoma.