Team Approach: Osteosarcoma of the Distal Part of the Femur in Adolescents

Abstract

Osteosarcoma, while rare, is the most common primary bone cancer and accounts for up to 10% of all new pediatric cancer diagnoses annually in the United States. Most commonly, osteosarcoma affects the distal femur and occurs as a high-grade intramedullary (conventional) subtype. Patients with osteosarcoma are treated with a multi-disciplinary team approach. Often, an orthopaedic oncologist initiates the workup after making a presumptive diagnosis based on classic clinical and radiographic findings. Advanced imaging and a tissue biopsy are obtained to evaluate the extent of disease and to histologically confirm the diagnosis. Musculoskeletal radiologists and pathologists are key team members who evaluate the imaging and tissue samples to make a definitive diagnosis, establish a prognosis, and help the clinicians develop a treatment plan. Medical/pediatric oncologists are essential team members who provide the appropriate neoadjuvant and adjuvant chemotherapy treatment and assist with long-term surveillance to monitor for local or distant relapse. Orthopaedic oncologists develop and execute a plan for resection of the tumor followed by appropriate reconstruction. The current standard of care for distal femoral osteosarcoma is neoadjuvant chemotherapy followed by limb salvage for the surgically resectable tumor, reconstruction of the bone and soft tissue defect, and adjuvant chemotherapy. The survival for patients with isolated osteosarcoma is approximately 70% and has not substantially improved in over 25 years.^–

Figure 1

High-grade intramedullary (conventional) osteosarcoma of the distal femur in a 12-year-old boy with knee pain and swelling. (a) Anterior-posterior and (b) lateral radiographs of the left knee demonstrate bone formation (black asterisk) and bone destruction. There is an associated large soft tissue component. The lesion results in periosteal reaction and elevation of the periosteum (Codman triangle) (white arrow). Note that the physes are open.

Figure 2

High-grade intramedullary (conventional) osteosarcoma of the distal femur in a 12-year-old boy with knee pain and swelling. (a) Coronal T1-weighted MRI without fat saturation of the left knee. White arrows identify the soft tissue component of the lesion. There is low T1 signal within the lesion corresponding to bone formation (white asterisk). The lesion extends to the physis (black arrow). (b) Coronal short-tau inversion recovery (STIR) MRI of the left knee demonstrates that the soft tissue component of the mass elevates the periosteum (white arrow). There is low STIR signal within the lesion corresponding to bone formation (white asterisk). Extensive peritumoral edema is noted (white hash sign). (c) Sagittal T2-weighted MRI with fat saturation of the left knee showing epiphyseal edema (black arrow). (d) Sagittal T1-weighted MRI of the left knee obtained after intravenous administration of contrast material reveals the extent of enhancing intramedullary and soft tissue components of the lesion (white arrow). There is enhancing peritumoral edema (black arrow). There is an area of necrosis (white asterisk) noted.

Figure 3

Pathology of a high-grade intramedullary (conventional) osteosarcoma. (a) At low-(100x, left) and intermediate (200x, right) magnification, the diagnostic biopsy reveals a cellular malignancy with conspicuous malignant osteoid formation (yellow arrow). The cellular component is composed of pleomorphic cells with osteoblast-like morphology. Increased mitotic activity (white arrow) and individual cell necrosis (gray arrow) are evidence of rapid cell turnover. (b) Gross images of the resected specimen (left) reveal an expansile mass centered in the medullary cavity with areas of hemorrhage and cystic degeneration (black arrows) and neoplastic bone formation (green arrowhead). In routine processing of these specimens, a complete cross section is blocked out (grid, small inset) and submitted for histologic processing to assess treatment response. The histologic findings in the resection specimen (right) are typical of treated osteosarcoma. The cellularity is markedly diminished, with necrosis and neoplastic bone remaining. The marbled, irregular seams of osteoid have a paucicellular stroma and are distinct in appearance from the native, lamellar bone (blue arrowhead).

Figure 4

High-grade intramedullary (conventional) osteosarcoma of the left distal femur in a 12-year-old boy after neoadjuvant chemotherapy. (a) Anterior-posterior and (b) lateral radiographs of the left knee demonstrate extensive new bone formation (black asterisk). There is periosteal reaction (black arrows). Note interval increase in periosteal reaction as well as development of mineralization of the periosteum surrounding the soft tissue mass that often occurs with treatment (white arrow).

Figure 5

High-grade intramedullary (conventional) osteosarcoma of the left distal femur in a 12-year-old boy with distal femoral osteosarcoma after neoadjuvant chemotherapy. (a) Coronal T1-weighted MRI without fat saturation of the left knee. The lesion shows interval decrease in size of the soft tissue mass (black arrow). There are now new foci of increased T1 signal within the lesion consistent with hemorrhage (white arrow). An area of necrosis with hemorrhage and cystic change is seen in the medial metaphysis (white asterisk). (b) Axial T2-weighted MRI with fat saturation illustrating an area of necrosis with hemorrhage and cystic change with a fluid-fluid level (white arrow). There remains unchanged low T2 signal within the lesion corresponding to malignant bone formation (white asterisk). (c) Sagittal T1-weighted MRI of the left knee obtained after intravenous administration of contrast material reveals interval decrease in size of the soft tissue mass with decreased enhancing peritumoral edema and internal necrosis within the tumor after chemotherapy. (d) Sagittal T1-weighted MRI of the left knee obtained after intravenous administration of contrast material shows internal cystic change within the tumor.

Figure 6

High-grade intramedullary (conventional) osteosarcoma of the distal femur in a 12-year-old boy one year after chemotherapy and surgical resection. (a) Anterior-posterior radiograph of the left knee demonstrates interval resection of the distal femur and reconstruction with a cemented, mobile-bearing, modular, expandable distal femur endoprosthesis. (b) Cross-table lateral radiograph of the left knee demonstrates heterotopic ossification posterior to the femur at the bone prosthesis interface (white arrow).