A moderate Ts depletion (Fig. 4a) did not affect proliferation (Supplementary Fig. 4D), as we had previously determined from breast cancer cell lines, that TS needs to reduce beyond a threshold to diminish proliferation.12 Furthermore, Ts knockdown also did not hamper the growth of primary tumours from the cells subcutaneously injected in flanks of syngeneic mice (Fig. 4b). Here, TYMS is linked to breast carcinoma.