Although COX-2 inhibitors may attenuate breast tumor growth in preclinical models [16–22] and early phase I/II neoadjuvant trials, when used in combination with aromatase inhibitors [23, 24], the recent phase III, multicenter, double-blind, randomized REACT trial of celecoxib vs placebo showed no benefit in delaying time to progression or overall survival in primary breast cancer patients [25]. Here, CYP19A1 is linked to breast cancer.