Abstract:

A 77 year old female without a previous history of malignancy presented to our dermatology clinic for evaluation of a tender lesion underneath the left breast present for approximately 18 months. Exam demonstrated a 4cm ulcerated plaque in the left inframammary fold, with homogenous blue and white structures on dermoscopy. A biopsy was performed with concern for a pigmented basal cell carcinoma or melanoma. Subsequent histologic evaluation revealed atypical cells invading the dermis and dermoepidermal junction with focal extension into the epidermis. The tumor displayed marked epidermotropism and prominent melanin pigment. No prominent pagetoid involvement of the epidermis was identified. Angiolymphatic invasion was present. Immunohistochemical studies demonstrated that the tumor cells were negative for Sox10 and Melan-A, and positive for CK7 and GATA3, consistent with epidermotropic invasive ductal adenocarcinoma of primary breast origin. While Pagets disease is the most common breast malignancy to develop pigmentation, pigmented metastases of invasive breast adenocarcinoma have been reported in the literature as well. Prostate, lung, and medullary thyroid adenocarcinomas have also been reported to occur with pigmentation of cutaneous metastases, although with less frequency. Pigment deposition within metastatic breast adenocarcinoma is thought to be secondary to compromise of the dermal-epidermal junction and subsequent migration of melanophages within the tumor, or due to the presence of pigment within the tumor cells themselves. This case demonstrates a potential diagnostic pitfall where pigmented epidermotropic breast adenocarcinoma can potentially mimic invasive melanoma on histology. As such, clinicians and pathologists should recognize this association between adenocarcinoma of the breast and melanin deposition, and use immunostaining when evaluating suspicious pigmented lesions from this anatomic location.

Financial Disclosure:
No current or relevant financial relationships exist.

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Calvin Knapp III, MD