Metaplastic Breast Carcinoma with Secondary Paget Disease Occurring after Prophylactic Mastectomy: Diagnostic Considerations

Invasive mammary carcinoma occurring after prophylactic mastectomy is rare. We report a case of a 42-year-old female diagnosed with metaplastic breast carcinoma after prophylactic mastectomy. Previously, the patient underwent bilateral mastec to my followed by reconstruction for unilateral invasive mammary carcinoma. One decade later, she presented with a 10 cm mass in the contralateral chest wall. On subsequent wide local excision and axillary lymph node dissection, an invasive carcinoma with squamous differentiation was identified. Examination of the skin epidermis revealed Paget cells with squamous differentiation. Given that this malignancy was arising after prophylactic mastectomy, the differential diagnosis included primary breast carcinoma, contralateral metastatic breast carcinoma and squamous cell carcinoma. The final diagnosis was primary invasive ductal carcinoma with squamous differentiation (metaplastic carcinoma) involving the epidermis of the skin as secondary Paget disease. To our knowledge, this is the first report to describe a primary metaplastic carcinoma of the breast occurring after prophylactic mastectomy. With the recent trend of women with breast cancer choosing bilateral mastectomy over unilateral lumpectomy at increasing rates, our report provides a relevant discussion detailing the pathology work up and diagnostic considerations that apply to cases of invasive carcinoma after prophylactic mastectomy.