Tamoxifen resistance remains a major obstacle in the treatment of estrogen receptor (ER)‑positive breast cancer. In recent years, the crucial role of the epithelial‑mesenchymal transition (EMT) process in the development of drug resistance in breast cancer has been underlined. However, the central molecules inducing the EMT process during the development of tamoxifen resistance remain to be elucidated. In the present study, it was demonstrated that tamoxifen‑resistant breast cancer cells underwent EMT and exhibited an enhanced cell motility and invasive behavior. The inhibition of snail family transcriptional repressor 1 (Snail) and twist family BHLH transcription factor 1 (Twist) reversed the EMT phenotype and decreased the tamoxifen resistance, migration and invasion of tamoxifen‑resistant breast cancer cells. In addition, it was observed that the inhibition of epidermal growth factor receptor (EGFR) reversed the EMT phenotype in tamoxifen‑resistant MCF7 (MCF‑7/TR) cells via the downregulation of Snail and Twist. Notably, the EGFR inhibitor, gefitinib, decreased tamoxifen resistance, migration and invasion through the inhibition of Snail and Twist. On the whole, the results of the present study suggest that EGFR may be a promising therapeutic target for tamoxifen‑resistant breast cancer. Moreover, it was suggested that gefitinib may serve as a potent novel therapeutic strategy for breast cancer patients, who have developed tamoxifen resistance.
Keywords: ER‑positive breast cancer; Snai1; Twist; epidermal growth factor receptor; epithelial‑mesenchymal transition; gefitinib; tamoxifen resistance.