TYMS and neoplasm: Beyond proliferation imaging, we previously demonstrated that tumour cells can translocate the equilibrative nucleoside transporter (ENT1) to the cell membrane within minutes to hours in response to TS inhibition, allowing increased uptake of thymidine nucleosides—including 18F-FLT—via the salvage pathway for their activation by thymidine kinase 1 (TK1), resulting in a transient “flare” response [12].