The present inventors have found microRNAs which are strongly associated with stabilization of NRF2 in tumors, and an object of the present invention is to provide means for utilizing such miRNAs for the diagnosis and treatment of cancer. The inventors conducted screening of 470 microRNAs in a microRNA library by use of HeLa cells. As a result, 8 miRNAs each exhibiting a large decrease in miRNA activity as compared with a control miRNA, and 8 miRNAs each exhibiting a large increase in miRNA activity as compared with a control miRNA, were identified. The inventors have found that the NRF2 activation in the living body, in particular tumor cells, can be detected by use of the thus-identified miRNAs, whereby malignancy of a tumor, or the like can be differentiated. The inventors have also found that a nucleic acid including a miRNA sequence associated with reduction in the aforementioned ARE activity can be used as a cancer therapeutic agent.
