Precursor to metabolite: Capecitabine to Fluorouracil

Capecitabine is converted to Fluorouracil by CES → CDA → thymidine phosphorylase.

The pair

Capecitabine — Oral prodrug converted to fluorouracil preferentially inside tumor tissue.
Fluorouracil — Thymidylate synthase inhibitor; DPD deficiency makes it lethal.