Metastatic cutaneous plasmacytoma presenting as a perianal giant mass.

There are 4 types of plasma-cell neoplasia: classic multiple myeloma (MM), extramedullary plasmacytoma without MM, solitary plasmacytoma of bone, and plasma-cell leukemia. Cutaneous involvement may be seen in all 4 types of plasma-cell neoplasia. Specific cutaneous involvement in patients with MM is very uncommon. It usually occurs in late stages of MM as a reflection of increased tumor cell burden. Extramedullary plasmacytoma (EMP) of the skin is a well-recognized, extremely rare, occurrence in MM. Extramedullary plasmacytomas of the skin can be divided into primary cutaneous plasmacytoma (PCP) and metastatic cutaneous plasmacytoma (MCP). Primary cutaneous plasmacytoma is defined as monoclonal proliferation of plasma-cells that arises primarily in the skin without evidence of systemic disease. In contrast to PCP, MCP arises from lymphatic or vascular spread of tumour or, more frequently, by direct extension from underlying bone lesions. Chest, back and abdomen are the most frequently involved areas followed by face, scalp, neck and extremities. Unusual localizations have been described related to MCP, including scrotum, eyelid and tongue. In literature, no cases of MCP presenting as a perianal giant mass have ever been reported. To our knowledge, we describe the first case of MCP located on the perianal area.