The following databases were searched from 1970 until 2020: Medline via PubMed, Cochrane Library and Web of Science with the MeSH terms of “Aromatase Inhibitors”, “Breast Cancer”, “Aromatase Inhibitors-associated arthralgia”, “autoimmune rheumatic diseases”, “musculoskeletal disorders”, “hormonal anti-estrogen therapy”, “endocrine therapy”. This evidence concerns the gene CYP19A1 and breast cancer.