Mammary Paget disease in Darier disease: beware the wolf in sheep's clothing.

This case describes new onset mammary Paget disease arising in the background of Darier disease. Clinically and histologically, lesions of Darier disease can mask the lesions of mammary Paget disease. A high index of suspicion is necessary to diagnose Paget disease in a patient with Darier disease, for a potentially fatal disease could easily be missed.