Periosteal Osteosarcoma

The Union for International Cancer Control (UICC) TNM classification of malignant tumors does not recommend that the TNM staging system for bone tumors be applied to surface/juxtacortical osteosarcoma or juxtacortical chondrosarcoma. However, other staging systems, such as the American Joint Committee on Cancer (AJCC) TNM system, do include these tumors in the bone staging system. See also the information on staging in section Bone tumors: Introduction.

Very rare cases in large series of osteosarcomas have been genetically studied, but no consistent anomaly is documented. In some cases, more-complex chromosomal alterations and point mutations in TP53, similar to those seen in high-grade osteosarcoma, are recorded.

The tumor, in continuity with the inner periosteum, has a demarcated lobulated broad-based ovoid appearance and is attached to the surface of the cortex, elevating the outer periosteum, producing a fusiform architecture. Cortical thickening may be conspicuous, with the mass causing cortical scalloping. The tumor comprises lobulated pale glistening cartilaginous tissue. Reactive bone spicules emanating from the cortex may be visible, and a delineated surface capsule derived from the periosteum is usual.

The tumor comprises poorly delineated lobules of cytologically atypical cartilage with intervening bands of primitive sarcomatous cells in which bone formation is present. Atypical fibroblastic areas may occur. Perpendicular periosteal reaction may be present, corresponding to the hair-on-end reaction seen on conventional radiographs. Primitive-appearing undifferentiated mesenchymal cells with nuclear atypia and mitoses prevail at the perimeter of the tumor. In cartilaginous areas, transition to osteoid matrix occurs.

Immunohistochemistry
SATB2 immunoexpression does not distinguish chondroblastic osteosarcoma from high-grade chondrosarcoma and is unhelpful in diagnosis.

Differential diagnosis
Periosteal chondrosarcomas occur in older individuals, are metaphyseal in distribution, have coarse calcification, and contain large lobules of well-differentiated hyaline cartilage. Tumor bone is absent. Parosteal osteosarcoma exhibits a protuberant mushrooming architecture arising from outer layers of the periosteum and is fibroblastic, with more mature appearing bone formation. High-grade surface osteosarcoma has anaplastic high-grade features throughout, with distribution and demographic status similar to those of conventional osteosarcoma.

Not clinically relevant

Periosteal osteosarcoma has a better prognosis than conventional osteosarcoma, with disease-free survival rates of 89% at 5 years and 77–86% at 10 years. Marrow involvement, originally thought to preclude the diagnosis, is rare and may predict more-aggressive behavior: cases without marrow involvement show a trend towards a better outcome at 5 years. Wide excision is optimal. Local recurrence, metastasis, and death usually occur within 3 years of diagnosis. Chemotherapy, although frequently used, does not appear to influence prognosis or survival. Assessment of postchemotherapy necrosis is not predictive of outcome. Occasional patients treated with chemotherapy developed a second malignancy.

MDM2/CDK4 amplification and IDH mutations have not been identified.

Essential: bone tumor with compatible imaging; surface location under the periosteum; intermediate-grade, largely chondroblastic osteosarcoma.