Functional Genetic Polymorphisms in the Aromatase Gene CYP19 Vary the Response of Breast Cancer Patients to Neoadjuvant Therapy with Aromatase Inhibitors

Abstract

Aromatase (CYP19) is a critical enzyme for estrogen biosynthesis, and aromatase inhibitors (AIs) are established endocrine therapy for post-menopausal women with breast cancer. DNA samples were obtained from 52 women pre-and post-AI treatment in the neoadjuvant setting. 82 breast cancer and 19 normal breast samples were resequenced to test the hypothesis that single nucleotide polymorphisms (SNPs) in the CYP19 gene might contribute to response to neoadjuvant AI therapy. There were no differences in CYP19 sequence between tumor and germline DNA in the same patient. Forty-eight CYP19 SNPs were identified, with four being novel when compared with previous resequencing data. Genotype-phenotype association studies performed with levels of aromatase activity, estrone, estradiol and tumor size pre-and post-AI treatment indicated that two tightly linked SNPs, rs6493497 and rs7176005 in the 5'-flanking region of CYP19 exon 1.1, were significantly associated with a greater change in aromatase activity after AI treatment. A follow-up study in 200 women with early breast cancer treated with adjuvant anastrozole showed that these same two SNPs were also associated with higher plasma estradiol levels pre-and post-AI treatment. Electrophoretic mobility shift and reporter gene assays confirmed the potential functional effects of these two SNPs on transcription regulation. These studies provide insight into the role of common genetic polymorphisms in CYP19 in variation in response to AIs by breast cancer patients.