Vaccine-associated sarcoma

From Wikipedia, the free encyclopedia

A vaccine-associated sarcoma (VAS) is a type of malignant tumor found in cats that has been linked to certain vaccines. VAS has become a concern for veterinarians and cat owners alike and has resulted in changes in recommended vaccine protocols. These tumors have been most commonly associated with rabies and feline leukemia virus vaccines.

1 History and pathology
2 Diagnosis
3 Treatment and prognosis
4 Precautionary measures
5 External links
6 References

[edit] History and pathology

VAS was first recognized at the University of Pennsylvania School of Veterinary Medicine in 1991.<ref name=Creegan>Creegan, Catherine (Nov-Dec 1997). "The sarcoma scare: making sense of feline vaccines - although there is some evidence that vaccines can cause skin cancer, most vets still recommend that cats be vaccinated - Brief Article". Animals. Retrieved on 2006-08-27.</ref> An association between highly aggressive fibrosarcomas and typical vaccine location (between the shoulder blades) was made. Two possible factors for the increase of VAS at this time were the introduction in 1985 of vaccines for rabies and feline leukemia virus that contained aluminum adjuvant, and a law in 1987 requiring rabies vaccination in cats in Pennsylvania.<ref name=Kitchell>Kitchell, Barbara E. (2005). Feline Vaccine-Associated Sarcomas. Proceedings of the 30th World Congress of the World Small Animal Veterinary Association. Retrieved on 2006-08-27.</ref>

Inflammation in the subcutis following vaccination is considered to be a risk factor in the development of VAS, and vaccines containing aluminum were found to produce more inflammation.<ref name=O'Rourke>O'Rourke, Kate (2004). "Researchers probe vaccine-associated feline sarcoma". Journal of the American Veterinary Medical Association 225 (6). Retrieved on 2006-08-27.</ref> Furthermore, particles of aluminum adjuvant have been discovered in tumor macrophages.<ref name=Hershey>Hershey, Elizabeth A.; Sorenmo, Karen U.; Hendrick, Mattie J.; Shofer, Frances S.; Vail, David M. (2000). "Prognosis for presumed feline vaccine-associated sarcoma after excision: 61 cases (1986–1996)". Journal of the American Veterinary Medical Association 216 (1): 58-61. Retrieved on 2006-08-27.</ref> Similar examples of sarcomas developing secondary to inflammation include tumors associated with metallic implants and foreign body material in humans, and sarcomas of the esophagus associated with Spirocerca lupi infection in dogs and ocular sarcomas in cats following trauma. The incidence of VAS is between 1 in 1000 to 1 in 10000 vaccinated cats and has been found to be dose-dependent.<ref name=roundtable> (2005) "Vaccine-Associated Feline Sarcoma Task Force: Roundtable Discussion". Journal of the American Veterinary Medical Association 226 (11). Retrieved on 2006-08-27.</ref>

[edit] Diagnosis

VAS appears as a rapidly growing firm mass in and under the skin. The mass is often quite large when first detected and can become ulcerated or infected. Diagnosis of VAS is through a biopsy. The biopsy will show the presence of a sarcoma, but information like location and the presence of inflammation or necrosis will increase the suspicion of VAS. It is possible for cats to have a granuloma form after vaccination, so it is important to differentiate between the two before radical surgery is performed. One guideline for biopsy is if a growth is present three months after surgery, if a growth is greater than two centimeters, or if a growth is becoming larger one month after vaccination.<ref name=roundtable/>

X-rays are taken prior to surgery because about one in five cases of VAS will develop metastasis, usually to the lungs but possibly to the lymph nodes or skin.<ref name=Hershey/>

[edit] Treatment and prognosis

Treatment of VAS is through aggressive surgery. As soon as the tumor is recognized, it should be removed with very wide margins to ensure complete removal. Treatment may also include chemotherapy or radiation therapy. The most significant prognostic factor is initial surgical treatment. One study showed that cats with radical (extensive) initial surgery had a median time to recurrence of 325 days versus 79 days for cats with marginal initial excision.<ref name=Kitchell/>

[edit] Precautionary measures

New vaccine protocols have been put forth by the American Association of Feline Practitioners that limit type and frequency of vaccinations given to cats. Specifically, the core vaccines for feline panleukopenia, feline viral rhinotracheitis, and feline calicivirus should only be given every three years to adult cats and the vaccine for feline leukemia virus should only be given to kittens and high risk cats. Also, vaccines should be given in areas making removal of VAS easier.<ref name=protocol>Eigner, Diane R.. Feline Vaccine Guidelines. The Winn Feline Foundation. Retrieved on 2006-08-27.</ref> A new canarypox vector rabies vaccine is on the market that is non-adjuvanted and creates little inflammation at the injection site.<ref name=Lappin>Lappin, Michael R. (2004). Feline vaccines. Proceedings of the 29th World Congress of the World Small Animal Veterinary Association. Retrieved on 2006-08-27.</ref>