ESR1 and breast carcinoma: After 2 weeks of incubation with 5 nmol/L paclitaxel, the number of colonies formed by ZR‐75‐1 and MCF‐7 cells in the E2 group was higher than that in the control group (Figure 1B), suggesting that E2 could promote the proliferation of ER+ breast cancer cells to make them resistant to paclitaxel.