CYP19A1 and breast cancer: During the treatment history period, 77.2% of patients had received ET, most frequently fulvestrant (37.2%) or nonsteroidal aromatase inhibitors (letrozole, 32.1%; anastrozole, 21.0%), and 40.7%, 20.2%, and 16.4% had received anticancer drugs, radiotherapy, and breast cancer surgery, respectively (Table 1).