MMP9 and retinoblastoma: A number of mechanisms are responsible for the enhanced expression of MMP-2 and MMP-9 in retinoblastoma, and thus the promotion of proliferation, invasion, migration of retinoblastoma cells: these include Wnt/β-catenin, NF-κB, PI3K, and Akt pathway activation, the upregulation of HMGA2 gene expression, as well as elevated expression of suppressor of Zeste 12 homolog (SUZ12), a component of the polycomb group protein [60,61,62,63,64].