Osteosarcoma

Dr Henry Knipe and A.Prof Frank Gaillard et al.

Osteosarcomas are malignant bone forming tumors and the second most common primary bone tumor after multiple myeloma. They account for ~20% of all primary bone tumors and occur in primary and secondary forms, each with different epidemiology and distribution. Although plain radiography can provide a lot of information, MRI is used for local staging by assessing intraosseous tumor extension (e.g. growth plate/epiphysis) and soft-tissue-involvement. Chest CT and bone scanning have a role in distant staging.

Osteosarcomas can be either primary or secondary, and these have differing demographics:

  • primary osteosarcoma: typically occurs in young patients (10-20 years) with 75% taking place before the age of 20 because the growth centers of the bone are more active during puberty/adolescence 3; slight male predominance
  • secondary osteosarcoma: occurs in the elderly; usually secondary to malignant degeneration of Paget disease, extensive bone infarcts, post-radiotherapy for other conditions, osteochondroma, and osteoblastoma

Patients often present with bone pain, occasionally accompanied by a soft-tissue mass or swelling. At times, the first symptoms are related to pathologic fracture.

The distribution of primary and secondary osteosarcomas is also different. 

  • primary tumors typically occur in the metaphyseal regions of long bones, and have a striking predilection for the knee, with up to 60% occurring there
  • secondary tumors, on the other hand, have a much wider distribution largely mirroring the combined incidence of their underlying condition, and thus much have a higher incidence in flat bones, especially the pelvis (a favourite site of Paget disease)

Osteosarcomas can be divided into a number of subtypes according to the degree of differentiation, location within the bone, and histological variants 3

These subtypes vary in imaging findings, demographics and biological behavior, and include:

Macroscopically osteosarcomas are bulky tumors where a heterogeneous cut surface demonstrates areas of hemorrhage, fibrosis and cystic degeneration. Their extension within the medullary cavity is often much more extensive than the bulky part of the tumor would suggest. Areas of bone formation are characteristic of osteosarcomas, with the degree of bone formation varying widely.

Microscopically poorly formed trabecular bone is seen with (in the typical high-grade conventional subtype) cellular pleomorphism and mitoses. Variable amounts of fibrocystic and chondroblastic appearing cells may also be encountered. 

They typically occur at the metadiaphysis of tubular bones in the appendicular skeleton. Common sites include:

  • femur: ~40% (especially distal femur)
  • tibia: ~16% (especially proximal tibia)
  • humerus: ~15% 

Other less common sites include:

Serum alkaline phosphatase (ALP) may be raised (particularly with advanced disease).

Conventional radiography continues to play an important role in diagnosis. Typical appearances of conventional high-grade osteosarcoma include:

The role of CT is predominantly utilized in assisting biopsy and staging. CT adds little to plain radiography and MRI in the direct assessment of the tumor. The exception to this rule is predominantly lytic lesions in which small amounts of mineralised material may be inapparent on both plain film and MRI 4.

MRI is proving an essential tool to determine accurate local staging and assessment for limb-sparing resection, particularly for evaluation of intraosseous tumor extension and soft-tissue involvement. Evaluation of the growth plate is also essential as up to 75-88% of metaphyseal tumors do cross the growth plate into the epiphysis 4.

  • T1
    • soft tissue non-mineralised component: intermediate signal intensity
    • mineralised/ossified components: low signal intensity
    • peritumoral edema: intermediate signal intensity
    • scattered regions of hemorrhage will have a variable signal (see aging blood on MRI)
    • enhancement: solid components enhance
  • T2
    • soft tissue non-mineralised component: high signal intensity
    • mineralised/ossified components: low signal intensity
    • peritumoral edema: high signal intensity

Work-up includes local staging by MRI (for skip lesions) prior to biopsy and distant staging with bone scan and chest CT.

Cure, if achievable, requires aggressive surgical resection often with amputation followed by chemotherapy. If a limb-salvage procedure is feasible, a course of multidrug chemotherapy precedes surgery to downstage the tumor, followed by wide resection of the bone and insertion of an endoprosthesis. The outcome depends on different factors such as age, sex, site, size, and type but the most important predictor is the histologic degree of necrosis post induction chemotherapy; 90% histologic necrosis is associated with much better prognosis 6. Currently, the 5-year survival rate after adequate therapy is approximately 60-80% 4.

The most frequent complications of conventional osteosarcoma are a pathologic fracture and the development of metastatic disease, particularly to bone, lung and regional lymph nodes.

General differential considerations include:

When the lesion is at the posteromedial distal femur consider:

When planning to biopsy a potential sarcoma, the treating surgeon should be consulted to plan the biopsy track as this will require excision to reduce the chance of seeding. A poorly planned track that crosses compartments can result in a more extensive resection, potentially with poor outcomes for the patient. 

Bone tumours

The differential diagnosis for bone tumors is dependent on the age of the patient, with a very different set of differentials for the pediatric patient.

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Article information

rID: 1170
Synonyms or Alternate Spellings:
  • Conventional osteosarcoma
  • Osteogenic sarcoma
  • Osteosarcoma: general
  • Osteosarcomas
  • Osteogenic sarcomas
  • Conventional osteosarcomas

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Cases and figures

  • Figure 1: IIlustration - distribution
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  • Case 1
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  • Figure 2: gross pathology - cut slice
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  • Case 2: with pathological fracture
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  • Figure 3: histology - H&E
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  • Osteosarcoma CT
    Case 3
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  • Case 4
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  • Case 5: with limb sparing surgery
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  • Case 6: with pathological fracture
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  • Case 7: humerus
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  • Case 8
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  • SAG T1 post
    Case 9: femur
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  • Case 10: fibula
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  • Case 11: gnathic osteosarcoma
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  • Osteosarcoma
    Case 12
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  • Contrast CT
    Case 13: of maxilla
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  • Case 14
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  • Case 15: arising in Paget disease
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  • Case 16
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  • Case 17
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  • Case 18: post irradiation osteosarcoma of skull base
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  • AP view
    Case 19
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  •  Case 20
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  • Case 21
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  • Case 22: gnathic osteosarcoma
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  • On axial post con...
    Case 23: sternal osteosarcoma
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  • Case 24
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  • Case 25
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  • Case 26
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  • Case 27
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  • Case 28
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