Clear-Cell Sarcoma With an Unusual Presentation Mimicking Metastatic Melanoma

Clear-cell sarcoma (CCS) was first described in 1968. It partly overlaps morphologically, immunohistochemically, and ultrastructurally with malignant melanoma (MM), hence its name "soft tissue melanoma." Nevertheless, there are sufficient cytogenetic differences between cutaneous melanoma and clear-cell sarcoma to consider clear-cell sarcoma as a separate entity. Clear-cell sarcoma of soft tissue is different from clear-cell sarcoma of the kidney. It is classified as a tumor of uncertain differentiation in the WHO 2020 classification of soft tissue tumors. It is an aggressive, rare malignant tumor that is involved in the deep soft tissues of the extremities and trunk. We report a case of primary clear-cell sarcoma of unusual presentation in a 31-year-old young man, mimicking metastatic melanoma. A 31-year-old man presented with a heel mass of 2.5 cm. Histologically, it was a dermal and hypodermal nodular proliferation of spindle cells of 23 mm with a grenz zone under the epidermis. There was no necrosis area or lymphovascular invasion. Surgical margins were free. There were no clinically suspicious lymph nodes. The tumor cells were stained for S100 protein, MELAN A, and HMB45, which led to an initial diagnosis of metastatic malignant melanoma. However, analysis by fluorescence in situ hybridization (FISH) found a rearrangement of the Ewing sarcoma region 1 (EWSR1) gene, which led to a diagnosis of primary clear cell sarcoma in the skin. This case highlights the importance of considering the diagnosis of a clear-cell sarcoma in front of any dermal lesions with morphological and immunohistochemical melanocytic features that do not have an in situ component and of atypical presentation, especially in young patients, hence the interest in performing fluorescence in situ hybridization for EWSR1, which remains the key to the diagnosis of cutaneous clear-cell sarcoma.