Cells deficient in thymidine kinase (TK) due to the mutation TK+/- TK-/- are resistant to the cytotoxic effects of the pyrimidine analogue trifluorothymidine (TFT).
Celice brez timidin-kinaze (TK) so zaradi mutacije TK+/- TK- /- odporne proti citotoksičnim učinkom pirimidinskega analoga trifluorotimidina (TFT).