Primary Clear Cell Sarcoma of Bone: Report of a Case Arising from Distal Femur in a Pediatric Patient and Review of the Literature

Clear cell sarcoma is a rare mesenchymal tumor with melanocytic differentiation, firstly described by Enziger in 1965. It accounts for less than 1% of all soft tissue sarcomas and occurs predominantly in the extremities of adults. Primary clear cell sarcoma of bone is even rarer; current literature consists of only 13 cases with a mean age of presentation of 45-year-old, ranging from 18 to 81. Because of the overlapping expression of melanocytic markers, the differential diagnosis should be addressed with metastatic malignant melanoma and metastasis from clear cell sarcoma of soft parts. Essential for the diagnosis is the evidence of translocations t (12;22) or t (2;22) resulting respectively in EWSR1/ATF1 and EWSR1-CREB1 gene fusion. Clinical history and radiological assessment could help discriminate between bone or soft parts origin. We report an unusual case of clear cell sarcoma of distal femur involving a 13-year-old patient. Histological sections showed a malignant neoplasm composed of nests of uniform cells separated by fibrous septa, showing strong immunoreactivity for melanoma triple cocktail. Real Time-Polymerase Chain Reaction revealed the presence of the fusion product EWSR1-ATF1, confirming the diagnosis of clear cell sarcoma of bone. Our purpose was to revise the current literature in order to find common clinicalradiological features to this rare entity. To the best of our knowledge, our case is the first bone clear cell sarcoma arising from the distal femur in a pediatric patient described in the literature: it highlights the importance of considering this rare entity in the differential diagnosis of primary bone tumor, although extremely rare and of the use of molecular means to confirm the diagnosis.