SLC5A1 and cancer: We noted that among the five known glutamine importers, solute carrier family 1 member 5 (SLC1A5) [26–30] and solute carrier family 38 member 1 (SLC38A1) [31–34] were widely studied and are up-regulated in four and six types of cancer, respectively; two less studied importers, solute carrier family 38 member 2 (SLC38A2) [35] and solute carrier family 38 member 5 (SLC38A5) [36], are overexpressed in one and three types of cancer, respectively; and solute carrier family 38 member 3 (SLC38A3) [37] is not up-regulated in any cancer (Fig. 1a).