As is true of most cytologically atypical or cytologically malignant spindle cell tumors of skin, a correct diagnosis depends on the correlation of several observations. 

No age group is exempt, but this tumor occurs most frequently in patients in their 20's and 30's. Therefore, given a patient in such an age group who presents with a tumor resembling a squamous cell carcinoma of skin, the possibility of epithelioid sarcoma should be raised.

Although listed as a soft tissue tumor, this type of sarcoma can occur in the dermis or subcutis. These are very rare on the face or trunk, but almost any other site, including buttocks, genitalia, and scalp, may be involved. Most of the cases occur on the extremities, particularly the upper extremity.

Often lethal. Recurrences are very common. Metastasizes to lymph nodes or by blood stream. May metastasize to skin or produce satellites. Cutaneous tumors are prone to ulcerate.

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Pathology The differential diagnosis includes many cytologically atypical and cytologically malignant tumors of skin. In addition, the differential diagnosis includes necrobiotic palisading granulomatous diseases.

Architecture:

Solitary or multiple nodules may be present and these may have:

Scalloped pushing borders or
Diffuse infiltration of the adjacent connective tissue.
Fascicular patterns (uncommonly and only focally if present) particularly when there is perineural spread.
Small round foci of extension resembling ordinary granulomas.

Central necrosis or necrobiosis is very characteristic. The central material may be composed of necrotic tumor or altered connective tissue. Such foci must be distinguished from palisading granulomas or foci of necrosis in other tumors such as squamous cell carcinoma.
Sometimes the altered connective tissue may be composed of relatively acellular eosinophilic collagen.
 

Cytology:

Spindle cells and epithelioid cells are usually both present, but the proportion varies from tumor to tumor and within a given tumor. This combination raises the possibility of malignant melanoma, but the positive markers for keratin,  prominent necrosis, and lack of evidence of the radial growth phase of a melanoma help make the distinction.

Atypia may be minimal, moderate, or severe. The degree of atypia may be greater in recurrences.

The tumor cells, especially the epithelioid cells, may be confused with squamous cell carcinoma, particularly if there is much epidermal hyperplasia associated with ulceration. The age of the patient can be helpful in alerting one to the possibility of epithelioid cell sarcoma in such instances.

The tumor cells may be mistaken for histiocytes, particularly if there are chronic inflammatory infiltrates in addition to the sarcoma.
 

Immunohistochemistry:

Positive for vimentin and for low and high molecular weight keratins, but the degree of reactivity varies from tumor to tumor and within a given tumor. Other marker results including S-100, CD-34, desmin, and actin, have been variable, particularly in cases that did not have the classical H&E pathology of epithelioid sarcoma.

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