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A woman in her 60s presented with a solitary, indolent, erythematous plaque in the right axilla measuring 5 × 3 cm (Figure, A). She reported a slowly growing subcutaneous node in the right axilla that she had noticed for the first time 10 years ago, and for the past year, she had observed a progressive infiltration of the overlying skin. She also reported having experienced swelling in the right axilla during her pregnancy over 20 years ago that disappeared with lactation. However, since then she had mild episodic pain in her right axilla during her menstrual cycle. A punch biopsy specimen was obtained and histopathological analysis was performed (Figure, B-D).
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C. Heterotopic primary cutaneous breast carcinoma
Analysis of the skin biopsy specimen revealed a dermal tumor infiltrating the subcutaneous fat without epidermal involvement. Tumor cells were diffusely dispersed between collagen bundles and lined up in an “Indian file pattern.” They showed basophilic nuclei with scant cytoplasm (Figure, B). Immunohistochemical staining with pancytokeratin (AE1/AE3), cytokeratin 20, GCDFP15, estrogen receptor, and GATA3 antibodies were positive while synaptophysin, chromogranin, and S100-stainings were negative. Considering the clinical history and the typical growth pattern we first suspected a cutaneous metastasis of an invasive lobular breast cancer.
Staging (including chest, abdominal, and pelvic computed tomography scans, cranial and breast magnetic resonance imaging, mammography, and breast sonography) revealed no evidence of primary or secondary tumors. We excised the axillary tumor with a safety margin of 15 mm, as well as 3 sentinel nodes and 3 additional lymph nodes from the right axilla (in 1 of the sentinel lymph nodes, isolated cytokeratin8/18–positive tumor cells and MNF116-positive tumor cells were found). The excised tumor showed histopathologic changes analogous to the skin biopsy. In addition, there were multiple GATA3-positive and estrogen receptor–positive apocrine glands in close association to the diffuse tumor cell infiltration most likely corresponding to heterotopic mammary glands. Integrating histopathologic features, clinical presentation, and diagnostic workup, our final diagnosis was that of a primary invasive lobular breast carcinoma in heterotopic cutaneous breast tissue.
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Corresponding Author: Konstantin Dumann, MD, Department of Dermatology, University Hospital Leipzig, Philipp-Rosenthal-Str 23, 04103 Leipzig, Germany (firstname.lastname@example.org).
Published Online: March 28, 2018. doi:10.1001/jamadermatol.2017.5976
Conflict of Interest Disclosures: None reported.
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