Merkel cell carcinoma of the breast: A case report

Merkel Cell Carcinoma (MCC) of the breast is extremely rare, representing less than 1 % of all breast cancers. A 59-year-old woman with severe primary progressive multiple sclerosis (MS), on glatiramer acetate (Copaxone), presented with 1 month of progressive right breast swelling. Ultrasound revealed a large, irregular mass with associated dermal thickening; a subsequent ultrasound-guided biopsy was performed, revealing pathological features of MCC. A staging PETCT showed evidence of widely metastatic disease. MCC is associated with immunocompromised status and reactivation of Merkel Cell Polyomavirus. Interestingly, MS is associated with Epstein Barr Virus. The relationships between viruses, immune system dysfunction, and immune-modulating drugs - such as those to treat MS - require further research.