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Pacheco et al. J Cancer Metastasis Treat 2020;6:49 I http://dx.doi.org/10.20517/2394-4722.2020.85 Page 13 of 15

Diagnostic ancillary techniques
The diagnostic ancillary techniques are not clinically relevant for high-grade surface osteosarcoma.

Main differential diagnosis
The distinction between a high-grade surface osteosarcoma and dedifferentiated parosteal osteosarcoma
or extramedullary extension from a conventional central osteosarcoma does not carry prognostic or
therapeutic implications. Areas of low-grade fibroblastic osteosarcoma are found in dedifferentiated
parosteal osteosarcoma and absent in high-grade surface osteosarcoma. A considerable intramedullary
component argues in favor of a central conventional osteosarcoma.

Due to therapeutic and prognostic implications, the most important differential diagnosis is with periosteal
osteosarcoma as indicated in the paragraph on periosteal osteosarcoma.

Treatment and prognosis
Treatment and prognosis do not differ from those of central conventional osteosarcoma. Treatment is
preoperative chemotherapy followed by surgical resection. The overall 5-year survival rate ranges between
[3]
46% to 62% [49,50] . A poor response to neoadjuvant chemotherapy is associated with a poor outcome .
CONCLUSION
There are a variety of bone and, to a lesser extent, soft tissue entities that should be considered in the
differential diagnosis of primary tumors of the bone surface. These comprise a wide clinical spectrum of
neoplasms that can impose diagnostic challenges outside the setting of large referral centers, due to their
extremely low incidence and unawareness of their clinical, radiological, and often subtle microscopic
differences. A multidisciplinary and expert approach to diagnosis is mandatory.

DECLARATIONS
Acknowledgments
We would like to thank Fundación Martha Stella C. de Vallarino for financial support through a medical
educational scholarship to one of the authors (MP).

Authors’ contributions
Preparing the manuscript draft and capturing the microscopic images: Pacheco M
Reviewing the manuscript: Righi A
Writing, producing the illustrations, reading and approving the final manuscrip: Pacheco M, Righi A

Availability of data and materials
Not applicable.

Financial support and sponsorship
Not applicable.

Conflicts of interest
All authors declared that there are no conflicts of interest.

Ethical approval and consent to participate
Not applicable.

Consent for publication
Not applicable.