NUCLEOLIN and gastric cancer: Some of them present G4 structure and a notable example with several published articles is the AS1411, also known as AGRO100, a DNA aptamer capable to recognize nucleolin (NCL), a protein overexpressed in the surface of several cancer cell types (e.g., gastric cancer, B-cell chronic lymphocytic leukemia, cervical cancer, breast cancer, among others) [6,18,19,20,21].