GSTM1 and breast carcinoma: Among the polymorphisms studied in GSTs, Glutathione S-transferase Theta1 (GSTT1) and Glutathione S-transferase Mu1 (GSTM1) null polymorphisms, the homozygous genotype of which implies the total absence of the enzyme, has previously been related to breast cancer risk by our research team [16,17].