Down‐regulation of SOX17 expression has been detected in colorectal cancer, hepatocellular carcinoma, gastric cancer, lung and oesophageal carcinoma, among others.30, 31, 32 Hypermethylation of the SOX17 promoter correlates with a poor prognosis for several cancers, and provides important prognostic information in breast cancer patients.32 Recent studies have shown that SOX17 is also epigenetically silenced in circulating tumour cells isolated from the peripheral blood of patients with breast or gastric cancer, and can be used as a molecular diagnostic marker in early‐stage gastric cancer.32 This evidence concerns the gene SOX17 and breast cancer.