To the editor,

I wish to congratulate Kim and his colleagues for their article [1] in which they investigated the prognostic value of human epidermal growth factor receptor 2 (HER2) status and the efficacy of anti-HER2 therapy in patients with hormone receptor (HR)-positive mucinous carcinoma (MC) of the breast. A total of 2716 HR-positive MC patients were enrolled and followed up for a median 100.1 months. Of these, 2094 (77.1%) were HER2-negative and 228 (8.4%) were HER2-positive. They reported that HER2-positive status was associated with worse prognosis in HR-positive and node-positive MC. As authors mentioned that the type of MC (pure vs mixed) was not recorded. In our database, including 6528 invasive breast cancer patients, all HER2-positive MC cases were mixed MC with infiltrating ductal carcinoma (IDC) and mucinous pathology. This finding suggests correlation between HER2 overexpression in MC and IDC of the breast and sheds more light on further characterization of patients with HER2-positive MC of the breast.