SLC46A1 and neoplasm: TPS is then distributed in the interstitial tissue after direct leakage from the disrupted blood–brain barrier (BBB) or leakage by bulk flow into the interstitial fluid, called the enhanced permeability and retention effect, and is taken up into tumor cells by the transporter SLC46A1, which is a heme carrier protein that accumulates in the lysosomes of tumor cells [42].