Another large study based on the US Nurses’ Health Study II also failed to find an association of endometriosis with overall breast cancer but did find that endometriosis was associated with increased risk of ER+/PR– breast tumours (adjusted HR = 1.9, 95% CI: 1.44–2.50) (Farland et al., 2016). Here, ESR1 is linked to endometriosis.