microRNA-21 and its emerging role in tumor progression in systemic malignancies.

modulatory effects of miR-21on the expression of Sprouty2 protein [8]. Increased PTEN expression is also seen. A similar impact is seen in gastric malignancies. miR-21 expression is typically accentuated in gastric carcinomas. This in turn results in decreased expression of Serpini1 [9], which augments tumor progression. Cancer cell migration is also enhanced at the same time. In addition, PTEN expression is altered by miR-21 [10] and miR-21 down-regulates PDCD4 expression and thereby contributes to tumor progression and evolution. Not surprisingly, a significant association exists between tumor differentiation and miR-21 expression in gastric tumors [11]. A similar relationship is seen between the TNM stage and the miR-21 levels in circulating tumor cells [12]. It is obvious from the above examples that miR-21 plays a major role in tumor progression in gastrointestinal malignancies.