Finally, inactivation of different NHEJ-promoting factors that inhibit DNA end resection, such as 53BP1, RIF1, PTIP, Artemis, REV7 (MAD2L2), the Shieldin complex (SHLD1–3 and REV7), and the CTC1–STN1–TEN1 (CST) complex, can also lead to a partial restoration of HR in BRCA1-deficient cells and mammary tumors (Bunting et al. 2010; Callen et al. 2013; Chapman et al. 2013; Escribano-Diaz et al. 2013; Jaspers et al. 2013; Zimmermann et al. 2013; Wang et al. 2014; Xu et al. 2015; Barazas et al. 2018; Dev et al. 2018; Ghezraoui et al. 2018; Gupta et al. 2018; Noordermeer et al. 2018). This evidence concerns the gene MAD2L2 and breast cancer.