[Pigmented Paget's disease of the breast]

Pigmented Paget's disease of the breast is an uncommon disease. Histology shows intraepidermal pagetoid cells positive for cytokeratin7. We report a difficult case with an atypical clinic presentation as a pigmented lesion and unusual immunohistochemical results such as absence of expression of cytokeratin7 (CK7).

A 68-year-old woman presented a heterogeneous pigmented lesion on the left nipple extending to the areola, over a period of six years. Histologic study of biopsy showed intraepidermal proliferation of atypical cells positive for melanocytic markers but negative for CK7. The clinicopathological features were consistent with malignant lentigo. Nevertheless, histological study of the whole lesion after complete surgical excision was in favour of mammary Paget's disease, while CK7 remained negative.

Pigmented Paget's disease of the breast is infrequent, with only a few cases reported in the literature and is suggestive of malignant melanoma or pigmented metastasis of mammary adenocarcinoma. Immunohistochemistry is necessary, especially using CK7 staining, which is usually positive (sensitivity of almost 100%), except in some rare cases such as ours. In these difficult cases, study of a wider panel of antibodies may be necessary for diagnosis.