For the co-culture experiments, we used five different breast cancer organoids generated from patients with early stage or metastatic triple-negative breast cancer (ER−, PR− and human epidermal growth factor receptor 2-negative (HER2−)) or hormone receptor-positive (ER+ and/or PR+), HER2− breast cancer (Supplementary Table 2). The gene discussed is ESR1; the disease is breast carcinoma.