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Contact Information

Phone: 919.513.6690
Fax:  919.513.6669

Hours: Monday-Friday, 8AM-5PM
Regular appointments: 
Drop-offs:     7:30AM-8:30AM
Discharges:   4PM-6PM

The Oncology service is a referral-only service. Once the primary veterinarian calls and sets up the referral, the owner may call and arrange an appointment. If the patient has been seen by our service recently, owners may call Oncology directly to set up an appointment.

General Information

The Terry Center

red Cross Cadeceus

Emergency Service

Main Number: 919.513.6500
Small Animal Emergency: 919.513.6911
Large Animal Emergency: 919.513.6630
Monday-Thursday 5PM-8AM
Friday 5PM-Monday 8AM

Open 24 hours on legal holidays.
No appointment needed.


Vaccine-associated Sarcoma in Cats

What are Soft Tissue Sarcomas?

Soft tissue sarcomas are tumors originating from structural and connective tissues. They are most often evident as masses in the skin or subcutaneous tissues. Although seemingly diverse in their tissues of origin, these tumors share similar biologic behavior and are therefore considered together. Examples of soft tissue sarcomas include fibrosarcoma, malignant fibrous histiocytoma, and myxosarcoma.

Soft tissue sarcomas are locally invasive tumors and readily invade adjacent normal issues with finger-like projections. While they are locally invasive, spread to other places in the body (called metastasis) is less common; the overall metastatic rate is between 11-23%.

Diagnostic Testing

Diagnostic tests are recommended for all cats diagnosed with soft tissue sarcomas to determine which sites in the body are involved. These tests include:


There are several treatment options for soft tissue sarcomas. Ultimately the decision to pursue a particular treatment is based on the tumor location, stage, clients' wishes and consultation with a veterinarian or veterinary oncologist. The following is a list of commonly discussed treatment options:

Option 1 - Surgery Complete excision with adequately wide margins generally involves resection of approximately 3cm margins laterally and removal of one intact fascial plane deep to the tumor. When these margins can be achieved, surgery is generally considered the treatment of choice. Although in cats, this can be very difficult unless the tumor is very small or located on a distal extremity. Because of this difficulty, one study of vaccine-associated sarcomas reported a median time to recurrence of 3 months.

Option 2 - Surgery + radiation therapy This involves the combination of surgery to remove the obvious bulk of the tumor (macroscopic disease) + radiation therapy to destroy microscopic disease. If multimodality therapy is a possibility, we recommend that cats be evaluated before any surgery (i.e., with gross disease present) by both a radiation oncologist and a surgeon so that an ideal treatment plan can be formulated. Because of the need for very wide excision (relative to body size) to effectively treat these tumors, many cats are optimally treated with radiation therapy prior to surgical removal. In our hospital, radiation therapy consists of 16-19 treatments given on a Mon-Friday schedule. Potential side effects of radiation include an early, reversible reaction to rapidly dividing tissues (skin, hair) that develops midway through treatment and is generally very mild in cats. There is also the potential, although unlikely, for late irreversible side effects to slowly dividing tissues (bone, muscle, nerves, underlying organs). A CT scan is performed prior to radiation therapy to aid the radiation oncologist in planning treatment for the individual animal in a way that optimizes the effect against the tumor and minimizes the impact on adjacent normal tissues. With this combination, the risk of recurrence is decreased and delayed with median control times of approximately 19-20 months. In a study reported by NCSU, the impact of surgical margins when surgery was performed after radiation therapy was demonstrated. In cats where clean margins were achieved following radiation therapy, the median disease control was approximately 3 years, compared to approximately 10 months for cats with dirty margins.

Option 3 - Chemotherapy While generally used for tumors with a higher likelihood of metastasis, chemotherapy can be considered for cats with vaccine-associated sarcomas as another tool for targeting cancer cells. The drug of choice for treating soft tissue sarcomas is doxorubicin. It is given at 3-week intervals for a total of 4-6 treatments. Chemotherapy drugs work by targeting fast-growing cells; cancer cells divide faster and abnormally compared to normal cells. Because of this, chemotherapy preferentially destroys cancer and spares normal tissues. There is the potential for some normal tissues with rapid growth rates (intestinal lining, bone marrow, hair cells) to be transiently damaged by chemotherapy. However, our goal in treating cancer in animals is quality of life, so the dosages are lower than those used in people. We do not normally see significant toxicity with chemotherapy. There is always some risk when a drug is given for the first time, and the oncologist will discuss what types of side effects may develop and what to watch for. If the pet has no problems the first time they receive a drug, they should have no problems with subsequent treatments of that drug. If the pet experiences any side effects, we address them as needed and lower the dosage of the causative drug for future treatments to prevent recurrent problems. A unique side effect of doxorubicin is its ability to weaken the kidneys with multiple doses. Periodic blood tests will be done to monitor this.

Option 4 - Palliative radiation therapy If a tumor cannot be removed surgically, cannot be treated with the combination of surgery + radiation therapy, or if distant metastasis is identified, palliative radiation therapy can be considered. Palliative radiation therapy consists of two consecutive twice-daily doses of radiation therapy and is aimed at alleviating pain, inflammation, and swelling associated with the tumor. We recommend that the treatment be repeated in one month if no disease or symptom progression is noted in hopes of extending the duration of response.

Selected References

  1. Kass PH, Barnes WG JR, Spangler WL, et al. Epidemiologic evidence for a causal relation between vaccination and fibrosarcoma tumorigenesis in cats. J Am Vet Med Assoc 1993;203:396-405.
  2. Hendrick MJ, Shofer FS, Goldschmidt MH, et al. Comparison of fibrosarcomas that developed at vaccination sites and at nonvaccination sites in cats: 239 cases (1991-1992). J Am Vet Med Assoc 1994;205:1425-1429.
  3. Davidson EB, Gregory CR, Kass PH. Surgical excision of soft tissue fibrosarcomas in cats. Vet Surg 2001;26:265-269.
  4. Hershey AE, Sorenmo KU, Hendrick MJ, et al. Prognosis for presumed feline vaccine-associated sarcoma after excision: 61 cases (1986-1996). J Am Vet Med Assoc 2000;216:58-61.
  5. Cronin K, Page RL, Spodnick G, et al. Radiation therapy and surgery for fibrosarcoma in 33 cats. Vet Radiol Ultrasound 1998;39:51-56.
  6. Kobayashi T, Hauck ML, Dodge R, et al. Preoperative radiotherapy for vaccine associated sarcoma in 92 cats. Vet Radiol Ultrasound 2002;43:473-479.
  7. Cohen M, Wright JC, Brawner WR, et al. Use of surgery and electron beam irradiation, with or without chemotherapy, for treatment of vaccine-associated sarcomas in cats: 78 cases (1996-2000). J Am Vet Med Assoc 2002;219:1582-1589.
  8. Bregazzi VS, LaRue SM, McNiel E, et al. Treatment with a combination of doxorubicin, surgery, and radiation versus surgery and radiation alone for cats with vaccine-associated sarcomas. J Am Vet Med Assoc 2001;218:547-550.
  9. Barber LG, Sorenmo KU, Cronin KL, et al. Combined doxorubicin and cyclophosphamide chemotherapy for nonresectable feline fibrosarcoma. J Am Anim Hosp Assoc 2000;36:416-421.
  10. Poirier VJ, Thamm DH, Kurzman ID, et al. Liposome-encapsulated doxorubicin (Doxil) and doxorubicin in the treatment of vaccine-associated sarcoma in cats. J Vet Intern Med 2002;16:726-731.