TIMP3 and breast cancer: Accumulating evidence demonstrates that miRNAs contribute to the emergence of resistance to chemotherapeutic drugs, such as doxorubicin by regulating various targets in breast cancer.16, 17 Documents have also shown the role of microRNA‐221 in various types of cancers.7, 18, 19, 20, 21, 22, 23 For example, the downregulation of microRNA‐221 in human oral squamous cell carcinoma7 increased the sensitivity to adriamycin via regulation of TIMP3 expression.