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Soft Tissue Sarcomas
Lauren Askin Quarterman, DVM, DACVR (Radiation Oncology)

PetCure Oncology, San Jose, California

Etiology/Pathophysiology In dogs, sarcomas have been associated with radiation,
trauma, foreign bodies, implants, and the parasite
Soft tissue sarcomas (STS) are a group of tumors that Spirocerca lupi. In cats, three different types of sarcomas
arise from mesenchymal tissues. Tumors within this are seen: vaccine‐associated sarcomas (also referred to as
group tend to have different morphologic and histologic injection site sarcomas), viral‐induced sarcomas, and
features, but the biologic behavior is similar; therefore, nonviral nonvaccine sarcomas.
they are often treated as one. Several important biologic Vaccine‐associated sarcomas have been shown to be
features have been described: linked to the administration of inactivated vaccines,
ability to arise from any anatomic site such as feline leukemia virus (FeLV) and rabies. The
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appear pseudoencapsulated but tend to infiltrate development of sarcomas at sites of vaccine administra-
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through and along fascial planes tion with FeLV or rabies is believed to be between 1/1000
metastasize hematogenously in up to 20% cases, but to 1/10 000 cases. Some reports have shown an increased
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regional lymph node metastasis is unusual risk with increasing number of vaccinations and with
local recurrence after conservative surgery is common repeated vaccination at the same site. The time to tumor
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gross tumors generally have a poor response to chem- development at the site of vaccination has been reported
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otherapy and radiation therapy. to be four weeks to 10 years but most commonly occurs
between two and 10 months post vaccination. The
Not all lesions arising from the subcutaneous space are majority of injection site sarcomas in cats arise from
malignant, and many are often benign or inflammatory. vaccines, but it is important to keep in mind that there
Though histologic distinction is not clinically important in have been reports of tumor development at the site of
the treatment of these tumors, the nomenclature is deter- lufenuron and microchip injections. It is hypothesized
mined by the connective tissue (muscle, adipose, fascial, that the formation of these tumors is related to inflam-
fibrous, and neurovascular) from which they arise. Tumors mation created secondary to the injection. This is sup-
classified as STS include fibrosarcoma, peripheral nerve ported by the similar histologic appearance of injection
sheath tumor, myxosarcoma, liposarcoma, undifferenti- site sarcomas to tumors arising in the eyes of cats after
ated sarcoma, and malignant fibrous histiocytoma. Soft trauma.
tissue tumors such as osteosarcoma, chondrosarcoma, Viral‐induced sarcomas are rare. Typically, these mul-
hemangiosarcoma, rhabdomyosarcoma, histiocytic sar- ticentric tumors are seen in young cats that are positive
coma, nerve root/brachial plexus, oral sarcomas, and syn- for FeLV. FeLV can serve as a natural vector and trans-
ovial cell sarcoma are not classified as STS as they have a duce nonviral genetic elements from cat cellular DNA.
higher propensity for metastasis and/or local recurrence. This can result in the formation of a recombinant virus,
termed feline sarcoma virus (FeSV), which exhibits
altered oncogenicity. FeSV has been isolated from natu-
Epidemiology rally occurring fibrosarcomas of FeLV‐infected cats,
supporting the theory that FeSV can cause the transfor-
Soft tissue sarcomas comprise approximately 15% of all mation of cells and induce sarcoma formation in FeLV‐
skin and subcutaneous tumors in dogs and 7–9% in cats. positive cats.

Clinical Small Animal Internal Medicine Volume II, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical