ESR1 and breast cancer: This study may also aid risk stratification for SPCs in BC survivors, since we found significant evidence for variation in SPC risks in females by the age and calendar year at first BC diagnosis, the size, grade, morphology, estrogen receptor status or Human Epidermal growth factor Receptor 2 status of the first BC, the administration of chemotherapy, radiotherapy or hormonal therapy for the first BC, socioeconomic deprivation, and ethnicity.