Carcinoma en cuirasse mimicking dermatomal herpes zoster: A case report.

Carcinoma en cuirasse is a rare form of cutaneous metastasis, typically presenting with a sclerodermoid, infiltrated plaque, most commonly associated with breast cancer. In rare circumstances, carcinoma en cuirasse can mimic alternate etiologies including infectious, inflammatory or treatment-related dermatoses. We present the case of a 58-year-old woman with a 2-year history of stage IV metastatic estrogen receptor positive, progesterone receptor negative, HER2 negative breast carcinoma who developed a pruritic dermatomal eruption of her right flank that was initially empirically treated as herpes zoster without success prior to dermatology consultation. Subsequent skin biopsy revealed a "single file" dermal infiltration of epithelial cells, while immunohistochemistry for estrogen receptor demonstrated strong nuclear positivity, confirming the diagnosis of cutaneous metastasis. This case underscores the importance of considering carcinoma en cuirasse in patients with dermatomal eruptions in the context of known malignancy to ensure timely dermatology evaluation, prevent diagnostic delay and allow treatment escalation when necessary.