In a recent study, PDCD4 has been reported as a functional target of miR-21 in various aspects of tumor progression: cell proliferation, invasion, metastasis, and neoplastic transformation in breast cancer [27,29,30], invasion, intravasation, and metastasis in colon cancer [28], proliferation and invasion in esophageal squamous cell carcinoma [31]. The gene discussed is PDCD4; the disease is breast cancer.