Compared with tamoxifen monotherapy, the addition of a low dose of EZH2i increased the suppressive effects on six PDOs with different subtypes, including TNBC, Her2+ and Luminal B. This suggests that EZH2i combined with tamoxifen is a therapeutically actionable approach for breast cancer patients (Figs. 7J–M and S10). Here, ERBB2 is linked to breast cancer.