ESR1 and cancer: The summary RRs from the seven studies of breastfeeding show that breastfeeding was associated with reduced RRs of both ER+PR+ and ER-PR- cancer (summary RRs [95% CIs]: 0.95 [0.87–1.05] and 0.91 [0.83–1.00] for ER+PR+ and ER-PR- subtypes, respectively) (Table 4, Figure 3).