Small cell osteosarcoma
Updates to Article Attributes
Small cell osteosarcomas (SCOS) are a rare subtype of osteosarcoma characterised by the production of small round cells.
Epidemiology
Small cell osteosarcomasaccount for approximately 1.5% of osteosarcomas. They occur mainly in young adolescents with a mild female predilection but have been found in a wide age range1-4.
Diagnosis
Small cell osteosarcoma is a subtype of osteosarcoma. The diagnosis is based on a combination of pathological and typical imaging features like conventional osteosarcoma 1.
Diagnostic criteria
Diagnostic criteria according to the WHO classification of bone tumours (2020 - blue book) 1:
- imaging features of a bone tumour
- osteoid matrix with neoplastic bone formation
- permeative and destructive growth pattern
and in addition, the following is required:
- small blue round cell morphology
- focal osteoblastic bone formation
As with conventional osteosarcoma, high-grade atypia of tumour cells and frequent atypical mitotic figures are desirable features 1.
Clinical presentation
Clinical signs and symptoms are similar to those of conventional osteosarcoma and include pain and swelling 1,2.
Pathology
Small cell osteosarcoma is characterised by sheets of small round cells with focal neoplastic bone formation 1,2.
Aetiology
The aetiology is unknown 1.
Location
Small cell osteosarcoma has a similar distribution as conventional osteosarcoma but is more frequently seen in the diaphysis of long bones (up to 15%) 1.
Macroscopic appearance
Macroscopically small cell osteosarcoma looks like conventional osteosarcoma 1.
Microscopic appearance
Microscopically small cell osteosarcomas are characterised by the following histological features 1,2:
- small round to spindled tumour cells with scarce cytoplasm (high nuclear to cytoplasmatic ratio)
- focal, frequently lace-like osteoid formation
- round and oval nuclei
- mitoses readily present
ImmunohistochemistryImmunophenotype
Immunohistochemistry is similar to conventional osteosarcoma with an expression of SATB2, which might help in the differentiation from Ewing sarcoma 1,4. CD99 might be positive in some cases 3,4.
Radiographic features
Small cell osteosarcoma displays typical imaging features of an aggressive bone tumour with a mixed lytic and blastic and/or permeative destruction pattern periosteal reaction and soft tissue extension often similar to conventional osteosarcoma. However, they often display tumour osteoid calcification in the metaphysis and a non-mineralised more lytic appearance in a diaphyseal location resembling Ewing sarcoma 1-4.
Radiology report
The radiological report should include a description of the following:
- form and location
- tumour margins and transition zone
- cortical destruction
- soft tissue extension
Treatment and prognosis
Treatment of small cell osteosarcomas is most frequently similar to conventional osteosarcoma consisting of neoadjuvant chemotherapy and surgical resection with wide margins 1-4. Small cell osteosarcomas do not respond well to radiotherapy 4.
Prognosis of small cell osteosarcomas is slightly worse than the conventional form 1 with poor prognostic factors being a poor response to chemotherapy, positive surgical margins and metastatic disease 4.
History and etymology
Small cell osteosarcomas were first described by FH Sim in 1979 4,5.
Differential diagnosis
Small cell osteosarcoma mimics the appearance of conventional osteosarcoma, beyond that, it can look like the following tumours 1-3:
- Ewing sarcoma (no new bone formation)
- BCOR sarcoma
- lymphoma
- mesenchymal chondrosarcoma
-</ul><h5>Immunohistochemistry</h5><p><a title="Immunohistochemistry" href="/articles/immunohistochemistry">Immunohistochemistry</a> is similar to conventional osteosarcoma with an expression of SATB2, which might help in the differentiation from <a href="/articles/ewing-sarcoma">Ewing sarcoma</a> <sup>1,4</sup>. CD99 might be positive in some cases <sup>3,4</sup>.</p><h4>Radiographic features</h4><p>Small cell osteosarcoma displays typical imaging features of an aggressive bone tumour with a mixed lytic and blastic and/or permeative destruction pattern <a href="/articles/periosteal-reaction">periosteal reaction</a> and soft tissue extension often similar to conventional osteosarcoma. However, they often display tumour osteoid calcification in the metaphysis and a non-mineralised more lytic appearance in a diaphyseal location resembling <a href="/articles/ewing-sarcoma">Ewing sarcoma</a> <sup>1-4</sup>.</p><h4>Radiology report</h4><p>The radiological report should include a description of the following:</p><ul>- +</ul><h5>Immunophenotype</h5><p><a href="/articles/immunohistochemistry">Immunohistochemistry</a> is similar to conventional osteosarcoma with an expression of SATB2, which might help in the differentiation from <a href="/articles/ewing-sarcoma">Ewing sarcoma</a> <sup>1,4</sup>. CD99 might be positive in some cases <sup>3,4</sup>.</p><h4>Radiographic features</h4><p>Small cell osteosarcoma displays typical imaging features of an aggressive bone tumour with a mixed lytic and blastic and/or permeative destruction pattern <a href="/articles/periosteal-reaction">periosteal reaction</a> and soft tissue extension often similar to conventional osteosarcoma. However, they often display tumour osteoid calcification in the metaphysis and a non-mineralised more lytic appearance in a diaphyseal location resembling <a href="/articles/ewing-sarcoma">Ewing sarcoma</a> <sup>1-4</sup>.</p><h4>Radiology report</h4><p>The radiological report should include a description of the following:</p><ul>
References changed:
- 1. Baumhoer D, Böhling TO, Cates JM, Cleton-Janson AM, Hogendoorn PC, O’Donell PG, Rosenberg AE. Osteosarcoma. In: WHO Classification of Tumours Editorial Board. Soft tissue and bone tumours. Lyon (France): International Agency for Research on Cancer; 2020. (WHO classification of tumours series, 5th ed.; vol. 3). <a href="https://publications.iarc.fr/Book-And-Report-Series/Who-Classification-Of-Tumours/Soft-Tissue-And-Bone-Tumours-2020">https://publications.iarc.fr</a>
- 2. Edeiken J, Raymond A, Ayala A, Benjamin R, Murray J, Carrasco H. Small-Cell Osteosarcoma. Skeletal Radiol. 1987;16(8):621-8. <a href="https://doi.org/10.1007/bf00357110">doi:10.1007/bf00357110</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/3321462">Pubmed</a>
- 3. Bishop J, Shum C, Sheth S, Wakely P, Ali S. Small Cell Osteosarcoma. Am J Clin Pathol. 2010;133(5):756-61. <a href="https://doi.org/10.1309/ajcpo07vgdzcbrjf">doi:10.1309/ajcpo07vgdzcbrjf</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/20395522">Pubmed</a>
- 4. Zhong J, Hu Y, Si L et al. Clarifying Prognostic Factors of Small Cell Osteosarcoma: A Pooled Analysis of 20 Cases and the Literature. Journal of Bone Oncology. 2020;24:100305. <a href="https://doi.org/10.1016/j.jbo.2020.100305">doi:10.1016/j.jbo.2020.100305</a> - <a href="https://www.ncbi.nlm.nih.gov/pubmed/32775179">Pubmed</a>
- 5. Sim F, Unni K, Beabout J, Dahlin D. Osteosarcoma with Small Cells Simulating Ewing's Tumor. J Bone Joint Surg Am. 1979;61(2):207-15. - <a href="https://www.ncbi.nlm.nih.gov/pubmed/284009">Pubmed</a>
- 1. W. H. O. Classification WHO Classification of Tumours Editorial Board, Who Classification of Tumours Editorial. Soft Tissue and Bone Tumours. (2020-04-17) ISBN: 9789283245025
- 2. Edeiken J, Raymond A, Ayala A, Benjamin R, Murray J, Carrasco H. Small-Cell Osteosarcoma. Skeletal Radiol. 1987;16(8):621-8. <a href="https://doi.org/10.1007/BF00357110">doi:10.1007/BF00357110</a>
- 3. Bishop J, Shum C, Sheth S, Wakely P, Ali S. Small Cell Osteosarcoma: Cytopathologic Characteristics and Differential Diagnosis. Am J Clin Pathol. 2010;133(5):756-61. <a href="https://doi.org/10.1309/AJCPO07VGDZCBRJF">doi:10.1309/AJCPO07VGDZCBRJF</a>
- 4. Zhong J, Hu Y, Si L et al. Clarifying Prognostic Factors of Small Cell Osteosarcoma: A Pooled Analysis of 20 Cases and the Literature. J Bone Oncol. 2020;24:100305. <a href="https://doi.org/10.1016/j.jbo.2020.100305">doi:10.1016/j.jbo.2020.100305</a>
- 5. Sim F, Unni K, Beabout J, Dahlin D. Osteosarcoma with Small Cells Simulating Ewing's Tumor. J Bone Joint Surg Am. 1979;61(2):207-15. <a href="https://www.ncbi.nlm.nih.gov/pubmed/284009">PMID 284009</a>