Fig. 1

ESR1–CCDC170 fusion variants endow tamoxifen resistance in vivo. a The individual tumor growth curves of the T47D xenograft tumors expressing a vector, E2-E7, or E2-E10 ESR1–CCDC170 fusion variants with or without tamoxifen treatment (TAM). Athymic female mice prepped with estrogen (E2) pellets were injected with 1 × 10⁷engineered T47D cells and randomized into with/without tamoxifen treatment groups when the tumor volume reached 150–200 mm³. Vector, pLenti7.3 vector control. b The summarized tumor growth curves of the T47D xenograft tumors treated with or without tamoxifen as in a. **P < 0.01, ***P < 0.001 (based on two-way mixed ANOVA). The statistical significance comparing +/− tamoxifen within each tumor model: vector (P = 0.000007), E2-E7 (P = 0.003), E2-E10 (P = 0.151). The statistical significance comparing different models within tamoxifen-treated group are vector vs E2-E7 (P = 0.001) and vector vs E2-E10 (P = 0.000002). c The Kaplan–Meier curves for regression-free survival (tumor halving) of the engineered T47D xenograft tumors treated with tamoxifen. **P < 0.01, ***P < 0.001 (log-rank test)