SLC15A1 and neoplasm: When 5-ALA is administered exogenously, it can move into the cell by passive diffusion through the cell membrane8 or by active transport through several transporters that include the peptide transporters PEPT1 (SLC15A1) and PEPT2 (SLC15A2),9 the amino acid transporter PAT1 (SLC36A1)10 and BETA transporters.11 Whether these transporters facilitate increased uptake of 5-ALA in tumour cells compared with normal cells is unclear.