Five different polymorphisms in the CYP19 gene have been described in relationship to breast cancer risk, including the highly polymorphic tetranucleotide repeats in intron 5 [5-9], a C-T substitution in the 3' noncoding region of exon 10 [10], a cytosine to thymine substitution in codon 264 of exon 7 (resulting in amino acid Arginine to Cysteine substitution) [11], a silent G-A polymorphism at codon 80 in exon 3 [6], and a rare 3 base pair change within the promoter region of exon 1.4 [9]. This evidence concerns the gene CYP19A1 and breast cancer.