Enzymet thymidinfosforylase (ThyPase), som er involveret i den endelige omdannelse til 5- FU, findes i tumorvæv, men også i normalt væv, om end i lavere koncentrationer.
The enzyme involved in the final conversion to 5-FU, thymidine phosphorylase (ThyPase), is found in tumour tissues, but also in normal tissues, albeit usually at lower levels.