Dense Lichenoid Inflammation in Paget Disease: A Diagnostic Pitfall.

Mammary Paget disease is a rare form of breast cancer, which typically presents as an eczematous plaque on the nipple or surrounding skin. It is often a clinical diagnosis that is confirmed with skin biopsy. Histologic hallmarks of mammary Paget disease include large, pleomorphic, malignant, ductal epithelial cells within the epidermis. Chronic lichenoid inflammation may be seen in the papillary dermis but is not diagnostic. Because mammary Paget disease often overlies ductal carcinoma in situ or invasive carcinoma of the breast, prompt bilateral mammography is warranted. We report a case of Paget disease of the nipple with negative breast imaging that was originally misdiagnosed due to a dense lichenoid infiltrate obscuring the neoplasm.