ARID1A and ovarian cancer: To best discriminate between HGSOC and other ovarian cancer subtypes, we chose, on one hand, alterations characteristic of HGSOC, such as mutations in TP53 and BRCA1/2 as well as amplifications in C11orf30 (EMSY), CCNE1, MYC, PIK3CA and KRAS (ref. 5) and, on the other hand, mutations in a subset of genes recurrently altered by mutation only in other ovarian cancer subtypes (PIK3CA, PTEN, ERBB2, KRAS, BRAF, CTNNB1 and ARID1A).