However, miRNAs in general have been studied in oncology because they are often overexpressed in some cancers, as in the case of miRNA-21, and its predominant role in promoting cell invasiveness in renal cell carcinoma through the PDCD4/c-jun pathway (AP-1) [76,77] (Figure 1a). The gene discussed is PDCD4; the disease is renal cell carcinoma.