Background: Pigmented mammary Paget disease represents a rare variant of mammary Paget disease that clinically and dermoscopically simulates a melanoma. We report a case of pigmented mammary Paget disease mimicking a melanoma and describe the dermoscopic, reflectance-mode confocal microscopic, histological, and immunohistochemical features. Observations: A 70-year-old woman had a 5.5 x 4-cm pigmented plaque with a thin, scaly surface on her left breast; the plaque had slowly but progressively grown during the preceding 10 years. Dermoscopic examination showed a diffuse, light brown pigmentation with irregular black dots, small gray-blue structures, and irregular vessels. Confocal microscopic features, such as large reflecting cells with dark nuclei spreading upward in pagetoid fashion, were suggestive of melanoma. Histological evaluation integrated with immunohistochemical staining showed pigmented mammary Paget disease. Conclusions: This case demonstrates that the diagnosis of pigmented mammary Paget disease cannot be determined by clinical examination and dermoscopy alone. Therefore, immunohistochemical staining should be performed in growing lesions with equivocal clinical and dermoscopic aspects that are characterized by abundant pagetoid infiltration in hematoxylin-eosin-stained sections to avoid overlooking pigmented mammary Paget disease.
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