Answer: Epithelioid sarcoma

Histology: The specimen shows a multinodular mass with areas of necrosis associated with a high grade spindle cell tumor. In some areas, the tumor lacks a sarcomatous appearance but appears more epithelioid in nature with plump pleomorphic cells, prominent mitoses, and increased mitotic activity. Often in these areas, there is associated hemorrhage and necrosis. The lesion thus shows a biphasic appearance with some areas appearing sarcomatous and others appearing more epithelioid in nature.

Discussion: As in this case, the epithelioid sarcoma is a tumor of young adults and adolescents. It is a relatively uncommon tumor. The tumor usually occurs within the extremities, with the hands and the fingers being the most common sites of presentation. The tumor may occur superficially or it can sometimes be located deeper in the soft tissues and may involve tendon sheaths and aponeuroses. Multinodularity is typical of this tumor. The central necrosis and epithelioid appearance of the tumor cells can lead to a mistaken diagnosis of an infectious granulomatous process. The tumor is also often associated with an extensive desmoplastic reaction. The cells which appear epithelioid in nature are not truly epithelioid histiocytes but stain instead with cytokeratin. Immunohistochemistry can be helpful in establishing the proper diagnosis in this particular tumor. The tumor cells are positive for keratin, epithelial membrane antigen, vimentin, and CD34. On some occasions the tumor cells may also stain with CEA. The co-expression of keratin and vimentin is thought to be characteristic of this tumor.

The tumor can spread to other areas of skin, soft tissue, fascia and bone, and also by direct extension along fascial planes. They often recur locally, although these recurrences may occur after many years. Lymph node metastases are relatively common in this tumor, as well as metastases to lung and other areas. In some cases, lymph node metastasis may be the first clinical presentation of this tumor.