In CCC the HNF1B gene is upregulated by hypomethylation of its CpG island whereas, in high grade serous ovarian cancer, HNF1β expression is silenced via hypermethylation (Kato et al., 2008, Shen et al., 2013a), suggesting that HNF1β has a loss of function (tumour suppressor) role in high grade serous ovarian cancer but a gain of function (oncogenic) role in CCC (Gounaris et al., 2011, Shen et al., 2013b). The gene discussed is HNF1B; the disease is ovarian serous adenocarcinoma.