Not All That Produces Pigment Is Melanoma: Direct Epidermotropic Infiltration of Breast Carcinoma in a Woman With Melanin Incontinence Mimicking Pigmentary Disorders

Background: Local spread linked to breast carcinoma demonstrates a diverse spectrum of clinical presentations, including zosteriform, telangiectatic, and erysipeloid lesions. Pigmented epidermotropic infiltration resulting from breast carcinoma is seldom observed, occasionally posing diagnostic challenges owing to its resemblance to various other pigmentary disorders, such as malignant melanoma and other melanocytic lesions. Patient Presentation: A 47-year-old woman presented with complaints of a hyperpigmented, crusted lesion involving the nipple-areolar region of the left breast, which on histopathology revealed an invasive tumor involving the dermis, composed of discohesive cells arranged in single files and linear cords, extending directly into the overlying epidermis in a pagetoid pattern with extensive pigment incontinence. On employing a comprehensive panel of special stains and immunohistochemical markers, the presence of classic Paget cells was ruled out, and a final diagnosis of direct epidermotropic infiltration by underlying invasive lobular carcinoma (ILC) of the breast was found. Conclusion: Epidermotropic spread of ILC with associated pigment incontinence is a rare histopathological pattern that can closely mimic both pigmented mammary Paget disease and melanocytic disorders. The distinction is critical, as these entities differ significantly in their pathogenesis, prognosis, and management.