Abstract
Gastric cancer is a silent killer, claiming more than seven hundred thousand lives every year. This heavy burden creates an irrefutable need for accurate, noninvasive methods of population screening and early detection as well as disease monitoring and management. Gastric cancer is a multi-factorial disease with an uneven geographic distribution, mostly affecting the developing countries and Southeast Asia. The multi-dimensional roles of microRNAs in gene regulation and tumorigenesis have prompted investigators to explore their potentials in diagnosis and treatment of various cancers, including gastric cancer. In this respect, miR-21 has attracted much attention as well as generating some controversies. Here, we aim to describe, in a chronological order, the numerous studies which have explored 1) the interactions of this oncomir with Helicobacter pylori infection, as a class I gastric carcinogen, 2) its potential mechanisms of oncogenicity, by various induction/inhibition assays, and 3) its application as a diagnostic/prognostic invasive (tissue) and non-invasive (circulating) biomarker.