Despite the reported low levels of WEE1 expression in breast cancer, chromosome instability, that has also prognostic potential mainly in grade 2 tumors [89], may explain the effectiveness of WEE1 inhibitors, as supported by the predictive role of cyclin E. Our group and others showed that high PKMYT1 expression associates with reduced sensitivity to adavosertib, indicating a potential compensatory effect [35, 166]. This evidence concerns the gene CCNE1 and breast carcinoma.