BRCA1 and breast cancer: We found that, similar to loss of RAD18, UBC13 and PALB2, loss of RNF168 resulted in an increase in fork stalling in both BRCA1-deficient U2OS cells (Figure 4A, Supplementary S4A) and BRCA1-deficient breast cancer MDA-MB-231 cells (Supplementary Figure S1C, D).