In the treatment of cancer, aptamers can serve as free molecules targeting specific cancer biomarkers as either agonists or antagonists (Fig. 5).375 Both AS1411 and NOX-A12, which have reached the clinical trial stage, are antagonistic aptamers that specifically target nucleolin and CXCL12, respectively.376–379 Nucleolin is highly expressed in multiple tumor cells. Here, NUCLEOLIN is linked to cancer.