Because leucine (an activator of mTOR), glutamine (an essential amino acid for nucleotide biosynthesis and substrate for glutaminolysis), and arginine (an essential amino acid for tumor cells) are critical for the proliferation of ER-positive breast cancer cells, tumor cells may upregulate SLC6A14 to meet the increased demand for these amino acids [15]. The gene discussed is SLC6A14; the disease is breast carcinoma.