miR-4521 deficiency with its potential contribution to FAM129A upregulation might synergistically promote renal cancer cells’ malignant behaviors by enhancing MMP2/MMP9 through suppressing TIMP-1 and increasing their growth by escaping apoptosis through suppressing p53 by way of upregulation of MDM2 via a decreased Bax/Bcl2 ratio. The gene discussed is MDM2; the disease is renal carcinoma.