E2F1 and non-small cell lung carcinoma: MiR-661 level was positively correlated with E2F1 expression (r = 0.7822, P < 0.0001) in human NSCLC samples (Additional file 3: Figure S3), together with the results that E2F1 were upregulated with miR-661 overexpression in vitro (Fig. 5e) and in vivo (Fig. 5f), indicating that miR-661 may be involved in invasion of NSCLC through initiation of EMT by downregulating RB1 and upregulation of E2F1.