TYMS and breast cancer: On the other hand, GOF events of TYMS by means of copy number gains were found in 5-FU pretreated colon cancer patients (n = 44 out of 231) vs. untreated patients (n = 8 out of 121) (P < 0.05, Fisher exact test) (Supplementary Fig. 11), although this was not observed for breast cancer patients.