Finally, the lack of growth adaptation observed in non-macropinocytic HCC1569 cells on loss of ASCT2 (Fig. 6) suggests that in the other breast cancer cell lines (HCC1806, MDA-MB-231 and MDA-MB-468), macropinocytosis is playing a crucial role in cell proliferation by potentially sustaining the supply of glutamine. Here, SLC1A5 is linked to breast cancer.