ESR1 and cancer: Among postmenopausal women, there was no clear evidence for an association of HRT use with ESR1 A908G mutation-positive cancer (OR = 0.83, 95% CI = 0.28 to 2.42), but HRT use was inversely associated with mutation-negative breast cancer (OR = 0.62, 95% CI = 0.44 to 0.87 for ever users; OR = 0.64, 95% CI = 0.42 to 0.96 for duration of 5 or more years) (Table 2).