Uptake of [18F]FSPG in tumor cells is related to protein expression of the xCT transporter, a glutamate–cystine exchanger (SLC7A11/SLC3A2 (4F2hc) heterodimer) that transports L-cystine (Cys-S-S-Cys) into the cell and L-glutamate to the extracellular compartment [16]. The gene discussed is SLC7A11; the disease is neoplasm.