CYP19A1 and breast cancer: Taking aromatase inhibitors after tamoxifen (a “switch” strategy) reduced the recurrence rate significantly in comparison to 5 full years of tamoxifen (17% versus 19%); both the breast cancer-related mortality and the overall mortality were shown to be reduced (RR 0.84; 95% CI, 0.71–0.96; 2p-value = 0.015; (RR 0.82; 95% CI, 0.73–0.91; 2p-value = 0.0002) in favor of the “switch” strategy.