Metaplastic Breast Carcinoma Presenting as Cutaneous Spindle Cell Carcinoma

Abstract

Squamous cell carcinoma is one of the most common primary cutaneous carcinomas, but on rare occasion, metastatic squamous cell carcinoma from a distant site or solid organ can present as a cutaneous lesion. Most metastases to the skin present as dermal nodules or involve the dermal lymphatics, but when they are intimately associated with the epidermis, distinguishing the lesion as primary or metastatic may be extremely difficult and usually requires a clinical history or high index of suspicion. A 71‐year‐old woman presented with a history of breast carcinoma, status post radiation therapy and subsequent mastectomy. She developed multiple eruptive nodules over her mastectomy site, flank and back two years later. Histologically the lesions appeared to be arising from the surface epidermis and consisted of atypical, predominantly spindle cells, some of which streamed off of the basal layer of the epidermis. Following review of the mastectomy specimen material and performing additional immunohistochemical studies, it became clear that the origin of the carcinomas was metastatic from an underlying metaplastic breast carcinoma.