SLC1A5 and neoplasm: But since 18F-FACBC mainly relies on ASCT2 transport, which is expressed on the abluminal side of the blood vessels, this could further increase the uptake for 18F-FACBC compared to 18F-FET and 11C-MET in tumour tissue with a broken BBB, further increasing the TBR seen for 18F-FACBC.