Superficial paramucosal clear cell sarcoma of the soft parts resembling melanoma in a 13-year-old boy

Clear cell sarcoma (CCS) of tendons and aponeuroses, also known as melanoma of soft parts, represents an aggressive rare malignancy that is characterized by a nested or fascicular pattern of spindled cells and a pathognomonic reciprocal translocation, t(12;22)(q13;q12), that results in the fusion of EWSR1 and ATF1 genes. Numerous recent studies have recognized the importance of a cutaneous CCS variant that can mimic a broad spectrum of entities, including spindle cell melanoma, spindle cell squamous carcinoma, cutaneous leiomyosarcoma and atypical fibroxanthoma. We report a case of a 13-year-old boy with cutaneous CCS who presented with a few months history of an asymptomatic papule on the lower lip that was suggestive of a mucocele. Biopsy of the lesion showed a wedge shaped neoplasm arranged in nests and fascicles of epithelioid- to oval-shaped cells with pale cytoplasm, open chromatin and prominent nucleolus. The superficial component was closely opposed to the basal epithelium resembling the junctional nests of a melanocytic neoplasm. The process extended into and involved the striated muscle of the lip. The cells expressed S-100, CD99 and synaptophysin by immunohistochemistry, and there was focal HMB-45 and microphthalmia transcription factor (MiTF) positivity as well. Fluorescence in situ hybridization confirmed the presence of the t(12;22) (ESWR1-ATF1) translocation.