An inverse association was only found for estrogen receptor positive breast cancer (ER+ve) (5 SNP instrument, OR: 0.45, 95% CI: 0.20 to 1.01, P-value = 0.054, Q-value = 0.077; extended 10 SNP instrument, OR: 0.53, 95% CI: 0.35 to 0.82, P-value = 0.004, Q-value = 0.004), and not estrogen receptor negative (ER-ve) breast cancer (Table 1); although this heterogeneity by subtype was not statistically different (I2 = 16%; P-heterogeneity by subtype = 0.27). This evidence concerns the gene ESR1 and breast cancer.