TIMP3 and breast cancer: It is well documented that microRNAs have a significant effect on the management of various tumor progression.5, 6 For example, microRNA‐221 is up‐regulated in human oral squamous cell carcinoma, which induces cell proliferation via the modulation of TIMP3 expression.7 Moreover, miR‐665 has been reported to promote tumor metastasis by suppression of NR4A3 expression in breast cancer.8 However, the function of microRNA‐221 in the modulation of breast carcinoma resistance to chemotherapy is still unknown.