Female BC survivors diagnosed with grade 3, rather than grade 1, first BC were at increased non-breast SPC risks (HR: 1.08 (95% CI: 1.04–1.11)), whereas non-breast SPC risks were lower for those whose first BC was ER-positive rather than ER-negative (HR: 0.93 (95% CI: 0.89–0.97)) or HER2-positive rather than HER2-negative (HR: 0.88 (95% CI: 0.83–0.94)). Here, ESR1 is linked to breast cancer.