Salirasib or S-trans,trans-Farnesylthiosalicylic acid (FTS) is a salicylic acid derivative with potential antineoplastic activity. It acts as a potent competitive inhibitor of the enzyme prenylated protein methyltransferase (PPMTase), which methylates the carboxyl-terminal S-prenylcysteine in a large number of prenylated proteins including Ras. In such systems, Salirasib inhibits Ras methylation but not Ras farnesylation. Salirasib selectively disrupts the association of chronically active Ras proteins with the plasma membrane. Salirasib competes with Ras for binding to Ras-escort proteins, which possess putative farnesyl-binding domains and interact only with the activated form of Ras proteins, thereby promoting Ras nanoclusterization in the plasma membrane and robust signals. Salirasib was studied in the clinical trials in patients with solid tumors, however its development was discontinued.