A 13-year-old, previously healthy boy has had pain in the right leg for the past month. There is no history of trauma or recent illness. On physical examination, there is warmth and tenderness to palpation of the right lower thigh anteriorly, and the circumference of the right thigh is slightly larger than that of the left. His temperature is 39degC. A radiograph of the right leg shows a 6-cm expansile mass in the diaphyseal region of the right lower femur that extends into the soft tissue and is covered by layers of reactive bone. A biopsy of the mass is done, and microscopic examination shows sheets of closely packed primitive cells with small, uniform nuclei and only scant cytoplasm. Karyotypic analysis of the tumor cells shows a t(11;22) translocation. What is the most likely diagnosis?
The histologic appearance is characteristic of an Ewing sarcoma. The radiologic appearance of the mass in this child is typical for a malignant tumor, with bone destruction and soft-tissue extension. The two most common malignant bone tumors in children are osteosarcoma and Ewing sarcoma. Osteosarcomas typically arise in the metaphyseal region, whereas Ewing sarcoma arises in the diaphyseal region of long tubular bones, as seen in this case. This tumor usually occurs in patients 10 to 15 years old. The t (11;22) translocation is present in about 85% of Ewing sarcomas and the related primitive neuroectodermal tumors (PNETs), which belong to the small round cell tumors of childhood that can be difficult to distinguish microscopically. The translocation gives rise to the EWS-FLI1 fusion gene, now considered the definitive test for the diagnosis of these tumors. Ewing sarcomas often produce tender masses with fever and leukocytosis, mimicking acute osteomyelitis. Chondrosarcoma can occur across a wide age range, in contrast to most primary malignancies arising in bone, which occur most often in the first two decades; most are sufficiently differentiated so that a cartilaginous matrix is apparent on microscopic examination. A giant cell tumor is a benign but locally aggressive lesion that arises in the epiphysis of the long bones of young adults and has a "soap bubble" radiographic appearance. Metastatic carcinoma is the most common tumor of adults involving bone because there are far more carcinomas than primary bone malignancies; childhood bone metastases are rare. Osteosarcoma typically arises in the metaphyseal region, and the malignant spindle cells produce an osteoid matrix. A plasmacytoma produces a focal lytic lesion within the bone, and microscopically there are recognizable plasma cells.
Chondrosarcoma
Ewing sarcoma
Giant cell tumor
Metastatic carcinoma
Osteology