SLC1A4 and breast cancer: Serine is a small, neutral amino acid and can be imported into the cell by Na+-dependent transporters like ASCT1 (SLC1A4), which is upregulated in both breast cancer (Pollari et al., 2011) and lung cancer (Riscal et al., 2016), system A transporters like SNAT1 (SLC38A1), and the ASC system (El-Hattab, 2016).