CYP19A1 and breast cancer: In phase III pivotal randomized trials of CDK 4/6 inhibitors, Asians are underrepresented constituting 7.6–14.2% in first-line aromatase inhibitor-based trials for postmenopausal breast cancer indication and 21.0–32.0% in second-line fulvestrant-based trials or trials allowing premenopausal breast cancer [70–72] (Table 2).