Secondary osteosarcoma associated with osteofibrous dysplasia: a case report

Secondary osteosarcoma is a rare complication of primary malignancies and benign bone lesions. There are various types of diseases that cause secondary osteosarcoma.

"The present case is the first report of secondary osteosarcoma associated with osteofibrous dysplasia. During the long-term follow-up of osteofibrous dysplasia, oncologists should be aware of the possibility of secondary osteosarcoma" the authors commented.

The patient was a 15-year-old male who was in good health without any medical history. He was neither on any medication nor was there any history of malignancies or other diseases in his family. He was a student and was uninvolved in any specific occupation. He presented with pain and redness in the right lower leg. He was diagnosed with a bone tumor in the midshaft of the right tibia at the age of 2 years by a local doctor and treated.

Initially, the authors suspected Ewing sarcoma or fibrous dysplasia. Then bone biopsy and pathological examination was performed. However, hematoxylin and eosin staining was consistent with the characteristics of OFD, with which he was diagnosed.

The patient was followed up regularly from the age of 2 years. He had a pathological fracture of the right tibia at the age of 7 that was healed by closed reduction and casting only and did not require surgery. Then, he was followed up by a radiographic examination every 6 months, and natural bone growth was observed.

However, at the age of 15, he complained of swelling, heat, and pain in his right leg and was thus referred to our hospital. Radiography of the right tibia revealed longitudinal enlargement of the calcified lesion and erosion of the bone cortex. Furthermore, a periosteal reaction was observed along the tibial diaphysis . Magnetic resonance imaging (MRI) demonstrated an extensive existing malignancy lesion proximal to the marrow space of the tibial diaphysis (low intensity on the T1-weighted image and short T1 inversion recovery (STIR)). Thickening of the bone cortex was noted, but without apparent infiltration to the bone cortex. Extraosseous mass and perilesional edema that coincided with the swelling site in the shaft of the tibia were confirmed. Bone scintigraphy showed accumulation at the tumor site. When such findings are observed during the OFD follow-up, it is generally suspected to be a malignant transformation of the OFD. Therefore, an open biopsy was performed.

Pathological examination confirmed the diagnosis of chondroblastic OS. These results revealed there was concordance between radiological findings and histopathological findings, both showing features consistent with malignancy. Dense proliferation of spindle cells and formation of cartilage-like structures were observed. Hemoxylin and eosin staining shows the hyaline cartilage with severe atypia, which is the main pathological feature of chondroblastic OS. Furthermore, it appears to be a myxoid with single cells or delicate cords of cells indicating a more subtle atypia. The patient was therefore diagnosed with chondroblastic OS.

Treatment included preoperative chemotherapy (NECO95J, a widely used protocol for OS in the Japanese population) and surgical treatment. After preoperative chemotherapy, the radiograph showed ossification around the tumor. In addition, an MRI scan showed a reduction of the extraosseous mass and perilesional edema, which was diagnosed as a partial response. Subsequently, a wide margin resection was performed. Particularly, after osteotomy of the proximal tibia, an incision was made between the bone tumor, extraosseous mass, and perilesional edema (as observed on MRI), and the surrounding normal soft tissue. Subsequently, the lesion was treated with the pedicle freezing method, using liquid nitrogen after the osteotomy by intraoperative rapid pathological diagnosis. In particular, it was a state of R0 in the Residual tumor classification, as no tumor cells were found in the surgical margin macroscopically and microscopically. The proximal tibia was reconstructed using a double metal plate and the tibia was reinforced by transplantation of the right free vascularized fibula.

Chemotherapy was performed after surgical treatment according to the NECO-95 J protocol. The protocol consisted of cisplatin, doxorubicin, methotrexate, and ifosfamide. Pathological examination of the resected lesion revealed chondroblastic OS as on the preoperative diagnosis. No recurrence was observed at 2 years of follow-up.

Further reading:

Secondary osteosarcoma associated with osteofibrous dysplasia: a case report

Naohiro Oka, Kazuhiko Hashimoto et al

Skeletal Radiology

https://doi.org/10.1007/s00256-022-04122-5