Extracellular cysteine is also imported into cells through an alanine-serine-cysteine transporter and can be synthesized de novo via a trans-sulfuration pathway in some tissues (for example, liver, kidney, and pancreas), however, SLC7A11 remains an important transporter for cancer cells that are largely dependent on extracellular cystine for survival (6, 16). This evidence concerns the gene SLC7A11 and cancer.