Completely different from the membranous expression of AQP1 in myoepithelial cells of ducts in breast benign lesions and ductal carcinoma in situ (DCIS), we reported for the first time that AQP1 exhibited cytoplasmic expression pattern in cancer cells of invasive ductal carcinoma (IDC). This evidence concerns the gene AQP1 and invasive ductal breast carcinoma.