However, despite this defect in TOP2A, tumour subtypes characterized by a high frequency of ARID1A mutations, such as OCCC, have been reported to have relatively ‘flat' genomes (that is, relatively few large-scale genomic alterations/rearrangements)46 compared with other gynaecological malignancies such as high-grade serous ovarian cancers. Here, ARID1A is linked to ovarian serous adenocarcinoma.