An in vitro study reported that miR-221 may exert inhibitory effects towards bone marrow mononuclear cells and their abilities to proliferate, migrate and invade in childhood ALL cases, all by inhibiting the Wnt/β-catenin signaling pathway, as demonstrated by reduced PCNA (proliferating cell nuclear antigen), cyclin D1 and MMP9 (matrix metallopeptidase 9). This evidence concerns the gene MMP9 and acute lymphoblastic leukemia.