In addition to the previously mentioned importance of germline single nucleotide polymorphisms in CYP19A1 for the treatment of breast cancer patients with aromatase inhibitors, a recent study observed that more than 20% of patients treated with inhibitors acquired CYP19A1 amplifications [97], suggesting a counter-attack of tumor cells against this therapy in a significant portion of patients and a need for further optimization. Here, CYP19A1 is linked to breast cancer.