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Injection-Site Sarcoma 551

• Radiographs of the affected area may reveal • Hypofractionated radiation therapy (small PEARLS & CONSIDERATIONS
involvement of underlying bone. number of treatments) may be beneficial in Comments
VetBooks.ir Advanced or Confirmatory Testing • The role of chemotherapy in the treatment • Treatment of cats with injection-site sarcoma Diseases and Disorders
controlling incompletely excised tumors for
• Fine-needle aspiration of draining lymph
a significant period.
nodes to help rule out metastasis
is usually best performed using a team
• Histopathologic exam of an incisional of vaccine-site sarcoma is not well defined. approach. Specialists, including a surgeon,
oncologist, and radiation oncologist, should
Studies have not shown a definite advantage
biopsy specimen. Markers that may link the to using chemotherapy if local therapy be consulted early in the course of diagnostic
tumor with vaccine administration include (surgery, radiation therapy) is adequate. testing to determine the best multimodality
peripheral lymphocytic infiltrate and macro- Nevertheless, many oncologists recommend approach.
phages in the tumor that contain aluminum chemotherapy (doxorubicin, cyclophospha- • Many different types of sarcoma have been
adjuvant. In the absence of these markers, the mide, carboplatin, or ifosfamide). identified at vaccine sites.
location of the tumor, vaccination history,
and diagnosis of a sarcoma can suggest that Possible Complications Prevention
the tumor was caused by vaccination. • Complications of surgery can include wound • Early detection of tumors may lead to more
• Simple excisional biopsy is not recommended dehiscence and infection. successful treatment.
as a first step in obtaining a diagnosis for • Complications of radiation depend on the • Guidelines have been established by the
this tumor because the treatment is often location of the tumor in relation to critical American Veterinary Medical Association
inadequate. Reports suggest that aggressive normal structures (e.g., spinal cord, kidneys) (AVMA) Vaccine-Associated Sarcoma Task
surgical resection or multimodality therapy and the amount of radiation delivered to Force for approaching a cat that has a mass in
at the time of the first intervention is more those structures. an injection site after vaccination. According
likely to result in local disease control. • Chemotherapy complications (p. 152). to these guidelines, the following masses
• Advanced imaging (i.e., CT or MRI) can should be investigated with an incisional
delineate the local extent of the tumor. Recommended Monitoring biopsy to determine whether further diag-
Many of these tumors have a peripheral Due to the aggressive local nature of these nostics or treatment are necessary:
region that is contrast enhancing, with a tumors and the low risk of metastasis, long-term ○ A mass that is increasing in size 1 month
nonenhancing center. They also often have monitoring should include after injection
fingerlike projections that extend far into • Routine exam by a veterinarian to monitor for ○ A mass that is > 2 cm in diameter
surrounding normal tissues, and identifying local recurrence or side effects of treatment ○ A mass that persists > 3 months after
them helps with complete excision. • Routine thoracic radiographs to monitor for injection
pulmonary metastases • Vaccination of cats in areas of the body
TREATMENT that allow for aggressive surgical removal if
PROGNOSIS & OUTCOME a tumor develops (e.g., distal limb, tail) may
Treatment Overview prevent the tumors from requiring radia-
Treatment goals are to eradicate the local tumor • Prognosis depends on the stage and location tion or chemotherapy or from becoming
and, in some cats, to prevent or delay metastasis. of the tumor. life-threatening.
○ Cats with tumors that can be resected • Critical evaluation of vaccination protocols
Acute and Chronic Treatment with a wide margin of normal tissue for animals that have a low risk of contracting
• Radical surgical excision is the treatment of (tumors on the tail or distal limbs, small infectious disease may help decrease the risk
choice if physically possible. localized tumors) may have an excellent of vaccine-associated sarcomas.
○ Tumors on the distal limbs and tail may prognosis.
be successfully treated with amputation ○ Cats with larger tumors that can still Technician Tips
alone. be removed with aggressive surgery and Record the location of administration (which
○ Tumors on the trunk are usually not ame- are treated with multimodality therapy site) for each vaccine given to allow long-term
nable to radical excision. For these cases, (radiation, surgery, chemotherapy) may monitoring and follow-up of local adverse
a combination of radiation therapy and have an excellent prognosis for long-term reactions.
surgery (excision with as wide a margin tumor control; however, some of these cats
as possible based on physical exam and will develop metastases or recurrence of Client Education
advanced imaging) is usually indicated for the primary tumor. • Educate clients about the risks of tumor
successful treatment of the local tumor. ○ Cats with large nonresectable tumors or development after vaccination, as well as
○ Rarely, surgery with complete excision may metastases at the time of diagnosis have other risks of vaccination compared with
be possible and result in adequate local a poor prognosis regardless of treatment. the benefits of vaccination.
control of the tumor; however, in one • Another factor that affects recurrence of • Clients may also be educated on the impor-
report, 31% of cats with complete excision injection-site sarcoma is the extent of tance of examining their cats regularly for
of the tumor based on histopathologically surgery performed at the first intervention new masses to allow early detection and
clean margins developed recurrence. after identification of the tumor. Cats treatment of tumors.
• Radiation therapy before surgery allows that had the first excision of their tumors
adequate treatment of the microscopic at a referral institution had a longer time SUGGESTED READING
tumor extensions with smaller radiation to recurrence than cats that had surgery Liptäk JM, et al: Soft tissue sarcomas. In Withrow
fields; however, therapy interferes with the performed by their regular veterinarian. SJ, et al, editors: Withrow and MacEwen’s Small
histopathologic evaluation of the primary This is likely due to the relatively aggressive animal clinical oncology, St. Louis, 2013, Saunders,
tumor mass and the margins, and it may nature of surgery performed at the referral pp 356-380.
slightly increase risk of wound complications institutions. AUTHOR: John Farrelly, DVM, MS, DACVIM, DACVR
after surgery. EDITOR: Kenneth M. Rassnick, DVM, DACVIM

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