Primary cutaneous ewing's sarcoma/primitive neuroectodermal tumor: report of the first case diagnosed on aspiration cytology.

BACKGROUND: Extraskeletal Ewing's sarcoma (ES) was first recognized as a soft tissue tumor in 1975. Primacy cutaneous occurrence of Ewing's sarcoma/primitive neuroectodermnal tumor (ES/PNET) has been reported in only 31 cases so far. To the best of our knowledge, there is no report of preoperative cytologic diagnosis of cutaneous ES/PNET in the available literature except for this one.

CASE: A young adult presented with a recurrent swelling on the medial aspect of the left leg that had been present for the past 5 years. Fine needle aspiration cytology yielded cellular smears showing a small round cell tumor. Immunostaining on cell block material showed positivity for CD99, S-100 protein and neuron-specific enolase. A cytologic diagnosis of primary cutaneous ES/PNET was made. Local excision was performed, and the patient was well after 2 years of follow-up.

CONCLUSION: Primary cutaneous ES/PNET is a rare cutaneous tumor with a favorable clinical outcome. It can be diagnosed on cytology; however, immunocytochemistry is mandatory for differentiation from other small round cell tumors.