Since the recent findings of loss of claudin expression have mostly been linked to estrogen-negative and high-grade carcinomas20 and/or aggressive triple negative cases, it can be inferred that claudin-4 expression imbalance is related most exclusively to precursor lesions of highly aggressive tumors such as high-grade ductal carcinoma in situ.23 The gene discussed is CLDN4; the disease is ductal breast carcinoma in situ.