Next, we investigated MMP-9 and VEGF coexpression in retinoblastoma tissue, and demonstrated that MMP-9 and VEGF expression are positively correlated (r = 0.61, 95% CI 0.38–0.77, RE model; r = 0.59, 95% CI 0.34–0.77, QE model) (Additional file 3: Figure S3C). Here, MMP9 is linked to retinoblastoma.