Here, we adapted an established Cancer Intervention and Surveillance Network (CISNET) model to simulate life histories of multiple US female birth-cohorts diagnosed with stage 0-III ER+/HER2- breast cancer receiving different durations (none, 2.5, 5, 10 years) of two endocrine therapy regimens (aromatase inhibitors or tamoxifen; including ovarian-function suppression for premenopausal women). The gene discussed is ESR1; the disease is breast cancer.